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R/E/P => Klaus Heyne's Mic Lab => Topic started by: Noah Scot Snyder on June 09, 2016, 01:04:21 PM

Title: Telefunken/Schoeps m221
Post by: Noah Scot Snyder on June 09, 2016, 01:04:21 PM
My name is Noah Scot Snyder. I am a film scoring mixer in Los Angeles. I recently purchased two Telefunken/Schoeps m221b microphones from Madooma in Dortmund that came with CM9b capsules. I cannot find any information on these capsules at all. I contacted Bernhard Vollmer at Schoeps and he says he doesn’t know what they are but that the thinks they are NOT m221 capsules and most likely capsules from a m201 (I think they are not m221b capsules and predate them but not as far back as the m201). I can’t find mention anywhere of CM9b, CM9a or CM934a (which I know exist and threads to a m221a). Any information anyone might have would be greatly appreciated. The mics were listed in the sale as m221b but I think they are in fact m221 (made before the a/b/f distinction). I'm most interested in determining precisely what model m221 these are and what the lineage of the CM9b is (is it a precursor to the mk22?) Thank you.
Title: Re: Telefunken/Schoeps m221
Post by: panman on June 09, 2016, 07:09:02 PM
Hi Noah, like you said, there is no information to be found about those capsules. However I have a capsule like that, which is marked to be M155/2(there is a M155/1 too). It is omni and the same as MK22, but the thread only fits to the Telefunken M155 body. M155 was exclusively only made for Telefunken. I do not have any numbers of how many were made, but my M155 has the nr. 1467. M155 also has AC 701 tube, but the schematics are somewhat different.

But the problem here is, that your mics look like M221(the model before a/b/f, that was only made a short while). There should be M221 marked on them plus the serial numbers. My estimation is that c. 400 were ever made, because all serial numbers I have ever seen wheather live or in pics have been much below that(ok, I have seen about 10-15 only, so maybe I am wrong). So, please check that out and let us know, because the capsules in your pics do not fit to a M221 body.
Further more, please post a pic from the mic with the capsule removed, but showing the capsule end, that I am able to tell if it is M221 or M155 or something else again. Usually they are marked though. Pics from the innards would also clear a lot of things out.
Title: Re: Telefunken/Schoeps m221
Post by: Noah Scot Snyder on June 10, 2016, 03:26:53 PM
  Thank you Esa! These mics continue to be a journey of discovery. The sale listing indicated m221b but is is not m221b threading. The serial number is also enigmatic. One of the two bodies says "Nr. 1002" the other says nothing. There is no indication of model.
  I've attached some more pics including gut shots. It is definitely a AC701 but that's about all I can tell from inside. I also should mention I was able to obtain 2 more CM9b capsules so I have a total of 4 which are now being evaluated by a tech here in LA. I should also note that the mics look exactly like the m221 pictured on the product history section of the Schoeps website, which is part of the reason I guessed a m221 as the model. Thank you very much for your help and thoughts!

http://www.schoeps.de/en/history_products
(then click on 1954)

The guts seem to match this photo:
http://www.mikrofonbau.de/m221_e.htm
Title: Re: Telefunken/Schoeps m221
Post by: Noah Scot Snyder on June 10, 2016, 03:27:31 PM
More pics...
Title: Re: Telefunken/Schoeps m221
Post by: Noah Scot Snyder on June 10, 2016, 03:28:03 PM
...
Title: Re: Telefunken/Schoeps m221
Post by: Noah Scot Snyder on June 10, 2016, 03:28:36 PM
and finally.
Title: Re: Telefunken/Schoeps m221
Post by: panman on June 10, 2016, 05:20:28 PM
Ok, it`s very clear now: your pics from the guts show a M155 and definitely not a M221. The first link(http://www.schoeps.de/en/history_products) shows a Telefunken M155 and not M221 or M221A. The second link from the guts(http://www.mikrofonbau.de/m221_e.htm) also shows a M155 and notr M221 as it claims. The M934a capsule must be photoshopped on it, because M934a does not fit onto the M155 body. The thread-diameter of M155 is larger than that of a M221. The link also says both M221 and M155 have the same dimentions, but even that is not true, because M221 is considerably shorter than M155 and M221b. Never had a M221a in front of me, so I do not know about that, but I do have M155, M221 and M221b. Your mics are from an earlier badge and that`s why(I assume) the body looks the same as m221, but it is longer like M221b. My M155 does not have that Telefunken logo-ring but the logo etched. Mine is also clearly marked as M155.
The pic shows M221 above, M155 in the middle and M221 below.
Title: Re: Telefunken/Schoeps m221
Post by: panman on June 10, 2016, 05:22:39 PM
Same from the other side.
Title: Re: Telefunken/Schoeps m221
Post by: panman on June 10, 2016, 05:26:41 PM
Here the tubes:
Title: Re: Telefunken/Schoeps m221
Post by: panman on June 10, 2016, 05:30:19 PM
The threads: left M221, middle M155, right M221b. The differend thread sizes of M221 and M155 are clearly visible.

Title: Re: Telefunken/Schoeps m221
Post by: panman on June 10, 2016, 05:43:46 PM
M155 schematics redrawn and modified from M221b schematics. No idea what number 16 is.
Title: Re: Telefunken/Schoeps m221
Post by: panman on June 10, 2016, 05:59:43 PM
M221 schematics redrawn and modified from M221b schematics. Sorry for the stupid formats! You need to open the files to enlarge them. I somehow failed to convert them properly.
Title: Re: Telefunken/Schoeps m221
Post by: Noah Scot Snyder on June 10, 2016, 06:26:16 PM
Wow! Thank you for all that information and the schematics. I'd bet some of these changes between models came incrementally, meaning there are some obscure configurations. From your photos it certainly seems that the guts are of a m155. I think it's funny that those are pictured on the Schoeps site as examples of the m221, but I suppose they are all very closely related. It seems however that the threading on mine is the 221a type. The CM9b fits mine, at any rate, and I've found a CM934a so I'll be able to try that out soon. Perhaps the 934a on the m155 in the Schoeps photo was a CR3/1, I found the following photos from an old m155 sale on eBay.de. The secrets of these mics are slowly revealing themselves. They sound absolutely amazing on orchestra.
Title: Re: Telefunken/Schoeps m221
Post by: panman on June 10, 2016, 08:03:27 PM
If you have found a CM934a, it may well be that it fits your M155, but there are many Schoeps CM-capsules, that do not fit any of these M-mics. However what I have is a M934a. I guess that indicates another thread, but I am just guessing. The capsule on the link is clearly a 934a, but because the mic is a M155, it may be CM934a. I guess we`ll find out, when you get your CM934a and have tried out if it fits. The gut-pic on the link before is not showing a CR3/1, because it(CR3/1) does not have the cardioid-omni switch-ring, but the ring is clearly visible in the link. Just take a better look at the pics and you`ll see the difference. Again, I am just guessing, but I believe, that a CR3/1 in the pic is the same as the M155/3(cardioid) mentioned in the same link with the gut-pic.
Title: Re: Telefunken/Schoeps m221
Post by: Noah Scot Snyder on June 10, 2016, 08:24:14 PM
Again, thanks very much for your input. Indeed it is M934a capsule on its way to me and it sounds like you are saying that it will not fit. That's too bad as I was unaware of the two sizes of the 155/221 threadings. I just would like to have a couple cardioid capsules to compliment the omnis. Luckily these capsules are in such low demand that they sell for significantly less than new Schoeps capsules when you can find them. I guess I may end up with one to sell. I'm lucky to have gotten the two extra CM9b capsules and I'll keep a look out for others.
Title: Re: Telefunken/Schoeps m221
Post by: Noah Scot Snyder on June 18, 2016, 10:23:59 PM
Well, the plot thickens. I received the M934A and it fits just fine. I believe that may mean these microphones are the same as the microphone pictured in both links I posted previously. No photoshopping, I assure you. I still keep thinking that these mics are some version of the m221. The only thing I think I can say for sure is that they seem to be rare microphones indeed and they sound amazing.
Title: Re: Telefunken/Schoeps m221
Post by: Noah Scot Snyder on June 18, 2016, 10:25:34 PM
...
Title: Re: Telefunken/Schoeps m221
Post by: panman on June 19, 2016, 05:29:28 PM
I believe that may mean these microphones are the same as the microphone pictured in both links I posted previously. No photoshopping, I assure you. I still keep thinking that these mics are some version of the m221.

It really seems to be as you say, but they are all M155:s, because mine is definitely M155 and the insides look the same. I never had a chance to see a M221A. Neither is there any info or schematics to be found. It begs for the conclusion, that M221A and M155 are the same mic in fact. Would be nice to know for sure, though it would make some of my previous statements invalid. Is there really nobody, that owns a M221A? As to the M934A, that you now have, looking the pic you posted, I clearly see the thread diameter beeing bigger than in mine. Yours is marked M934A, but as I now checked mine, it only has "Nr 457" written on it. My conclusion is, that the first badge limited amount M221(no A or B) is the rare odd-ball with smaller thread and M155 and M221A share the same housing-tube and thread size. This link shows Telefunken M221, that is the same as mine: http://www.filmsoundsweden.se/backspegel/schoeps.html. There again the capsule only has the sn. marked. I would post pics, but my camera-battery just went flat. Of course they are all versions of M221, but as the schematics show, they do differ some bit.
Inspired by this thread, I mounted the M155 innards into a M221B body with M934B. The M221B housing has a larger inner diameter, so the electronics stay a bit loose, but with the set-screws it was possible to get it tight enough to do some AB:ing against the M221 having that 934-type capsule. There is a noticeable difference in volume M221 beeing louder, but M155 has better bass-response also extending lower. Otherwise they did not really differ much sonically. Did not check the trafo wiring yet. Could be the 50 versus 200 ohm difference. M221 has the phase flipped for some reason that I cannot figure out. Perhaps the European versus American standards differing those days. From before I do remember M221B beeing slightly louder than M221 again.
Title: Re: Telefunken/Schoeps m221
Post by: David Satz on June 20, 2016, 08:44:10 AM
I have only limited information about this, but there definitely was a model M 221 A, as well as an original M 221 which was neither "A" nor "B", and finally a model "C" was manufactured as a small, final batch many years later. There are differences in the mechanical fittings of the capsules (threads inside the body sleeve vs. threads outside, differing in pitch as well) and in the "A" type, the polarization voltage was generally 60 Volts while in the "B" type it was generally 120. However, there is at least one schematic published for the M 221 by Telefunken which seems to be a hybrid of "A" and "B" types. Perhaps as many as three variants of the "B" circuit were produced at different times.

Schoeps has only very limited internal documentation concerning many of their older products. The people who designed and built them are no longer available to be asked about them, and a fair amount of information has had to be reconstructed in retrospect. To complicate matters, Telefunken's documentation and product literature often doesn't track with Schoeps' as far as the use of the "A" and "B" is concerned, creating some curious anomalies and "time paradoxes".

--best regards
Title: Re: Telefunken/Schoeps m221
Post by: klaus on June 20, 2016, 01:34:28 PM
...in the "A" type, the polarization voltage was generally 60 Volts while in the "B" type it was generally 120.

Are you sure? It's been a while since I worked on them, but I don't recall such high voltage on the capsule. Maybe you meant B+, rather than capsule polarization voltage?

Title: Re: Telefunken/Schoeps m221
Post by: usattler on June 20, 2016, 08:11:27 PM
According to the schematics posted in this thread and elsewhere, at least the Telefunken M155 and the Schoeps M221B have their capsule biased by 120 V, the Schoeps M221 and M221A feature a 2:1 voltage divider and bias their capsule with 60 V. That fact may also be responsible for the level difference observed in a previous post.
Title: Re: Telefunken/Schoeps m221
Post by: Noah Scot Snyder on June 21, 2016, 11:23:04 AM
Thank you all for sharing your fine thoughts. With your help I am continuing to learn about these microphones. I may yet be able to rely on them for recording.
Title: Re: Telefunken/Schoeps m221
Post by: Noah Scot Snyder on November 18, 2016, 12:16:32 PM
Just wanted to happily report after replacing a faulty power supply (evidently a capacitor problem) these mics are finally quiet enough for me to us recording orchestra. I deeply appreciate all your help and I'm both lucky and pleased that the mics themselves are in such good condition.
Title: Re: Telefunken/Schoeps m221
Post by: klaus on November 18, 2016, 12:43:43 PM
Thanks for your Abschlussreport!
KH
Title: Re: Telefunken/Schoeps m221
Post by: Timjag on November 20, 2016, 06:49:26 PM
Out of interest does Martin at Madooma have any info on them? I recently bought a NOS W28 windshield for C28A from him and he was extremely helpful. He clearly has his resources for finding all this (lovely) old junk, I would have thought he would have some history on them.
Title: Re: Telefunken/Schoeps m221
Post by: klaus on November 20, 2016, 09:57:48 PM
Why not ask him directly?
Title: Re: Telefunken/Schoeps m221
Post by: Noah Scot Snyder on June 05, 2017, 11:35:13 PM
I did ask Martin, and Andreas Grosser as well as Berhard Vollmer and many other sources that were all generous with their knowledge, but no one had any info on the CM9b capsules or this version of the 221. They do sound great and I like the M934A capsule as well. It sounds different from my M221B with 934B capsule but has its own beautiful tone.
Title: Re: Telefunken/Schoeps m221
Post by: David Satz on November 30, 2019, 01:40:48 PM
As an update and partial correction: The M 221 had numerous sub-types and variants, each with several types of interchangeable capsules available. There were two physical attachment schemes: The original M 221, the M 221 A and the M 221 F used coarse threads that faced outward on the capsule housing. The M 221 B used fine threads that faced outward on the amplifier housing, like those of the Colette series today.

Meanwhile, either 60-Volt or 120-Volt polarization was used in different models of the series: The original M 221, most M 221 B, and all M 221 F used the 120-Volt plate supply to polarize the capsules. The M 221 A, the M 155, and a few Siemens-labeled M 221 B amplifiers used a voltage divider to bring this voltage down to 60 V, and of course the corresponding capsules were built to operate at that lower voltage.

[Edited later to state definitely what I have confirmed in the meantime:] The threads of the M 221 A and M 155 differed enough from those of the original M 221 to prevent capsules of either type from being used on the other type's amplifiers; Telefunken's brochure for the M 221 A says as much, and it means what it says. Since the M 221 A and M 155 capsules were designed for 60 Volt polarization while the original M 221 supplied 120 Volts to the capsules, it would be very bad particularly if capsules of the later type could have been used on the earlier type of amplifier.

--best regards

P.S. added later: The M 921/A capsule wasn't part of the M 221 series; it was the second-generation two-pattern capsule for the M 200 / M 201 / CM 55/R series. Thus while it fits on M 221 amplifiers, it was not designed for them, as the M 934 was. --best regards
Title: Re: Telefunken/Schoeps m221
Post by: David Satz on November 30, 2019, 02:58:30 PM
I re-read the whole thread and would like to add some further details.

--The M 155 was a version of the M 221 A sold to German broadcast organizations. It was distributed mainly by Telefunken. The only difference in principle between the two types was in how the shield and ground were wired at the T 3402 output connector: In the M 221 A, pin 3 = ground and pin 6 = shield, while in the M 155, pin 6 was left unconnected and the shield was tied to ground on pin 3.

The M 155 officially had only three capsule types available, called M 155/1, M 155/2 and M 155/3 (designations which were also applied to the microphones as a whole in some listings). Those corresponded to the M 221 A capsules M 939a, M 939b and M 940 respectively. The M 939a was a fully diffuse-field-equalized, single-diaphragm pressure transducer (omnidirectional) for what would be considered distant placement by today's standards (e.g. one microphone placed so as to pick up an entire orchestra or other large ensemble in mono, in a concert hall with natural balance), while the M 939b was also a single-diaphragm omni, but more like the types used today for A/B or "Decca tree" stereo recording, where the placement is not as distant.

The M 940 was a single-diaphragm, single-pattern cardioid capsule with a permanently attached ring flush with the front of the capsule, which was still needed to achieve the specified front-back ratio at that time. No counterpart of the M 934a switchable, two-pattern capsule--the "normal" offering for the M 221 A--was offered for the M 155 at all.

--"CM 9" is an internal Schoeps designation for a single-pattern omni capsule of a certain generation. I suspect that the CM 9a might correspond to the M 939a while the CM 9b might correspond to the M 939b. Please don't hold me to that, but if it's correct, then Bernhard Vollmer's idea that it was a forerunner of the MK 22 would also be correct--and I always enjoy agreeing with him.

--The "M 211" microphone shown in some photos earlier in the thread appears to have been chopped and rebuilt from its original form, in which there would have been a semi-flexible gooseneck about 8" long built in between the amplifier body and the large, RF-proof Tuchel output connector. I don't believe that the "foot" with the output connector in the photos is original.

--best regards
Title: Re: Telefunken/Schoeps m221
Post by: panman on December 01, 2019, 05:35:11 PM
David, thanks for reviving this thread and the incredible amount of new info!

You wrote:„I would also like to note that a fair amount of misinformation is evident in some of the messages.“

Perhaps you could be a bit more specific about it? I went through the thread, but was not able to find much except my initial assumption, that the pics the OP posted were M155:s, which proved not to be the case after seeing the pics in later postings, that made me suggest M155 is M221A. You finally confirmed, that they are "similar" except the way shield and ground were wired. I can confirm these differencies in my M155, but I do not have a M221A. However, my M221 has the same grounding scheme as M221A you mentioned. That means both schematics of M155 and M221, that I have posted in this thread have the grounds slightly wrong. I know it`s a long thread and and it`s hard to get all the details, but what else was misinformation, because „a fair amount of misinformation“ indicates there is some more? What did I miss?

Regarding the 60V/120V polarization, you say there is no way to know which. I find it hard to believe, that a company like Schoeps would take such a risk. In this thread I have pointed out, that the capsule-thread on the M221 is of a smaller diameter than the thread on the M155(M221A). I also posted pics from that. If  M155 and M221A are „identical“, that means there are three attachment-schemes for the capsules and not two. So, you cannot accidentally (or purpously) attach he capsule from M221A (M934a-60V) on the M221(120V)-body.  Schoeps surely did this on purpose. It remains the M221B, that according to you was sometimes polarized 60V, but mostly 120V. Based on what I wrote above, I would find it strange, that you really could mix 60 and 120V.capsules on M221B:s, but CV60/CM60 also came with 60 and 120V bodies and capsules and you can mix them. But at least they are sort of marked: 60V- capsules you can endlessly twist around, but 120V-capsules are fixed. One of the capsules I have turns around endlessly indicating a 60V-capsule, but inside it has a scratched writing: 120V, that is very hard to notice. Schoeps also marked the bodies with blue(120V) and red(60V) dots.
Title: Re: Telefunken/Schoeps m221
Post by: David Satz on December 01, 2019, 10:20:45 PM
Thank you for pointing out that the threads of the M 155 don't match those of the original M 221, which I wasn't aware of. [Edited later to add: I have since verified this directly.]

The question (for me) now is whether the threads of the original M 221 match those of the M 221 A. [edited later to add: No, they definitely don't.] There's an indication in one Telefunken document that they don't--actually, a literal statement that the capsules of the original M 221 series can't be used on M 221 A amplifiers. But to me that statement seemed as if it could have been a warning not to do something that was possible, rather than a warning that to do it was impossible.

So I will try to find that out first-hand if I possibly can--I hate relying on hearsay. (For example, even though I knew that an M 201's capsule head couldn't possibly fit onto an M 221 A amplifier, I actually tried it, for the sake of being able to say that I had tried it.)

Until then, I think it's best if I scale back the first of the two messages that I posted yesterday. I don't want to create false understandings or false issues. I also removed what I wrote about errors in earlier messages, since obviously I can and do make mistakes as well, sometimes right out in public.

--In general I can only surmise why Schoeps made some of the decisions that they made in the mid-1950s or, indeed, at other times. I have a fairly long list of "Schoeps mysteries" that I would like to solve. And even though I do occasionally find real answers (or what seem like real answers), that list just keeps getting longer.

--best regards
Title: Re: Telefunken/Schoeps m221
Post by: panman on January 07, 2020, 08:31:07 AM
I just found out, that the capsule in my M221 is the same as was used in the older model M201/ Telefunken ela M921. Comparing my capsule, that only has the sn with the capsule pictured here it looks exactly the same; just missing the "Umwegscheibe":

 https://www.ebay.de/itm/Telefunken-Ela-M921-Schoeps-M201-tube-microphone-with-capsule-Ela-M921-A/383335090745?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

I copied some of the text for the furure, because the link is not going to last forever:

“Please consider my description. You find only little information overall the world. This is all I found out.- -Offer for one original:- -1 x Telefunken Ela M921 >> Schoeps tube microphone M201 - -Serial number 0634- -On pic 2 you see 2 little holes in the body: Here was the telefunken label before- -There is scratched in the body: RIVA No 9- -This mic is equipped with the original capsule Ela M921- -The connector is a vintage 5 - pin plug- -The transformer for this mic is not inside. It must be outside. I have none of it.- -Once such a mic was modified with another plug and transformer by Andreas Grosser in Berlin- -Function:Capsule cannot be tested by myself.The body has a new Telefunken 6AU6 tube. - -Beside this tube there are only 4 resistors and 1 capacitor inside.- - If here is something defective, no problem to repair it. - -Also nothing is broken or does look damaged.”

The capsule here is labeled Ela M921/A, but I am sure there is a Schoeps name too. I am guessing it is M934, because I have seen pics of similar looking capsules having that marking without "A or B".
Title: Re: Telefunken/Schoeps m221
Post by: David Satz on January 08, 2020, 06:48:01 PM
panman, no, that would be a false conclusion. The M 921/A and M 934 were different capsules, not just different names for the same capsule. They were physically interchangeable, but the M 934 was built for 120 V polarization while the M 921/A was built for 150. There may also have been other differences between them; I hope to find that out sooner or later.

--Designations such as "Ela M 921" and "Ela M 201", etc. were clearly Telefunken nomenclature, but in these instances and a few others, Schoeps' internal designations were applied only to the "innards" of the amplifiers and capsules, and the public never saw them. Even in internal correspondence and notes, Schoeps often used the "M ..." designations for these models.

At the same time, however, Schoeps made other microphone types which were labeled with the company's own designations, such as the CM 51/9 and later the CM 61 and CM 60 series. And Telefunken distributed these microphones as well, using Schoeps' names for them (as they previously had done with the CM 51/3). I haven't discovered any guiding principle yet that determined which microphones got an "Ela M ..." designation and which ones didn't.

--best regards
Title: Re: Telefunken/Schoeps m221
Post by: RuudNL on June 05, 2020, 06:52:11 AM
I know that this is an old topic, but at the moment I have a defective Schoeps/Tele M221.

I found this schematic: https://repforums.prosoundweb.com/index.php?action=dlattach;topic=36988.0;attach=2568;image
Pin 2 of the connector has the filament voltage: +4 volts.
There is a voltage divider (#6: 100K and #5: 150K) that produces the grid voltage.

Assuming 4 volts filament voltage, the grid voltage would be 3/5 * 4 = 2.4 volts but....positive!
This seems very unlikely to me. In all cases I know of the grid is meant to be negative in reference to the cathode.

Am I missing something, or should te voltage on pin 2 be a negative 4 volts?
Title: Re: Telefunken/Schoeps m221
Post by: afterlifestudios on June 05, 2020, 01:43:26 PM
I am new to learning all this, but I think it's like the M49c which is grid leak biased, or "self biased" through a resistor from grid to cathode.  (I think that's #7, the180Mohm resistor on the m221 schematic.)

M49c schematic. https://io.groupdiy.com/file/gdiy-2017/u/39511/58d1402a040aa.bmp

This post I came across makes some sense for understanding grid leak bias:

"The key to understanding how grid-leaking biasing works is to dig deep into the physics of how a tube works. The heater heats the cathode. The cathode has a coating that, when heated, creates a cloud of electrons around it. Some of these electrons fall back into the cathode, some escape, and some bang into the nearby grid wire - not many, because, after all, nothing is attracting them (compared to plate B+). But there are some with high enough energy and direction to hit the grid wires and stay there. So now we have a grid with more electrons than it started with. If it were not for the resistor between grid and ground(cathode) the electrons would keep accumulating. But with this resistor the extra electrons have somewhere to go -- through the resistor and back to the cathode, so they are constantly bleeding off. Electrons flowing from the grid to the cathode (through the resistor) make the grid negative with respect to the cathode. Making the grid negative is biasing the tube."

Feel free to delete this if I'm way off track!

Title: Re: Telefunken/Schoeps m221
Post by: David Satz on June 05, 2020, 04:08:59 PM
Ruud, there were at least three different M 221 circuits, and Telefunken distributed them all--so the first thing you need to do is figure for sure which model you have. If it's an M 221 B, that should be engraved on the outer sleeve near the Tuchel connector. If it's an original M 221 (not A or B) then the outer sleeve will have a kind of "cigar band" carrying the Telefunken logo, embedded in a groove or depression within the housing.
Title: Re: Telefunken/Schoeps m221
Post by: panman on June 05, 2020, 05:24:00 PM
M155 schematics redrawn and modified from M221b schematics. No idea what number 16 is.

Two resistor-values 5 and 6 corrected.
Title: Re: Telefunken/Schoeps m221
Post by: RadarDoug2 on June 05, 2020, 05:30:16 PM
The cathode is more positive than the grid, because it is connected to the +4 volts.
Title: Re: Telefunken/Schoeps m221
Post by: RuudNL on June 06, 2020, 03:10:11 AM
Yes, you are correct! I overlooked the cathode connection. I had assumed that the cathode was connected to ground.
My wrong...