[Pryso]

While these models are interchangeable in many amps, I've read there are basic differences so they are not identical.

Looking through some spares I found a couple that confused me, possibly pulled from an old ST-70 some years ago.  They are Raytheon International, made in Japan, and labeled 6CA7/EL 34.  Obviously I don't know a great deal about tubes but I question why it would be labeled as both.  It looks like other EL34s I have with the more slender bottle than the 6CA7.

Any comments about this?

[decal]

Read this article from Brent Jessee's website. http://www.audiotubes.com/el34.htm

[FullRangeMan]

There is a EL34 chart, it need some zoom:

EL34 story in german:
http://www.jogis-roehrenbude.de/EL34-Story/EL34-Story.htm

[Pryso]

Thanks decal, the "from Brent Jessee's website" helped at least showing multiple tubes labeled EL34/6CA7.  I don't recall seeing that before but that may be my limited experience.

However I've been told the 6CA7 is a beam power tetrode while the EL34 is a true pentode.  So maybe my question is can they be intermixed in an amp if there are individual bias for each tube?

[FullRangeMan]

Thanks decal, the "from Brent Jessee's website" helped at least showing multiple tubes labeled EL34/6CA7.  I don't recall seeing that before but that may be my limited experience.

However I've been told the 6CA7 is a beam power tetrode while the EL34 is a true pentode.  So maybe my question is can they be intermixed in an amp if there are individual bias for each tube?

I could not use both el34 and 6ca7 in the same amp, not prob w/the Bias thou.
These tubes are different in the grid/screen, EL34 has independent grid/screen.
This difference is well used by Decware:
http://www.decware.com/newsite/paper146.html

[jea48]

Thanks decal, the "from Brent Jessee's website" helped at least showing multiple tubes labeled EL34/6CA7.  I don't recall seeing that before but that may be my limited experience.

However I've been told the 6CA7 is a beam power tetrode while the EL34 is a true pentode.  So maybe my question is can they be intermixed in an amp if there are individual bias for each tube?

However I've been told the 6CA7 is a beam power tetrode

Sure looks like a pentode to me.

6CA7 data sheet.
https://frank.pocnet.net/sheets/127/6/6CA7.pdf

//

EL34 data sheet.
Philips 1969
http://www.drtube.com/datasheets/el34-philips1969.pdf

1964 Mullard
https://frank.pocnet.net/sheets/129/e/EL34.pdf

Telefunken
http://www.telefunken-elektroakustik.com/products/tubes/black-diamond-tubes/EL34-TK-Tube-Data-Sheet.pdf

//

NOS Svetlana EL34/6CA7 data sheet.  See page 2.
http://tec-sol.com/products/tubes/svetlana/sv_tech_data.pdf

[Pryso]

jea48, I'm in over my head here which is why I ask.  All I can say is I was told the 6CA7 is a beam power tetrode by the Manley service tech.  I'm trying to sort out a biasing problem with a pair of Snapper monos - one is good, the other has erratic readings.  I moved the output tubes from the good reading amp to the other and it seemed to stabilize, based on the tech's suggestion.  So if that amp is OK now I'm trying to isolate which tube is affecting the biasing problem.  The only spares I have are marked 6CA7/EL34 which is why I ask if I can safely intermix those?

[G Georgopoulos]

Sure looks like a pentode to me.

6CA7 data sheet.
https://frank.pocnet.net/sheets/127/6/6CA7.pdf

 

[FullRangeMan]

A tube can be EL34 or 6ca7, but not both.
If it is labeled EL34 and 6ca7 in the same tube I would not buy or use this tube, very strange.
Its the same as a tube labeled 6550 and KT88.

[jea48]

jea48, I'm in over my head here which is why I ask.  All I can say is I was told the 6CA7 is a beam power tetrode by the Manley service tech.  I'm trying to sort out a biasing problem with a pair of Snapper monos - one is good, the other has erratic readings.  I moved the output tubes from the good reading amp to the other and it seemed to stabilize, based on the tech's suggestion.  So if that amp is OK now I'm trying to isolate which tube is affecting the biasing problem.  The only spares I have are marked 6CA7/EL34 which is why I ask if I can safely intermix those?

I didn't take the time to read for differences in the specs, tube characteristics, if any between the 6CA7 and the EL34 tubes. I only provided the data sheets.

So if that amp is OK now I'm trying to isolate which tube is affecting the biasing problem.

From the review article quote below each tube is individually biased. If the tubes from the other good amp are working fine in the amp you were having problems with, it would be a no brainer to me. I would buy a new quad of tubes for the amp. I would also spend the extra money for a matched quad. It's not that much more. 

Tubes are a whole lot cheaper than an output transformer.

Are you using the stock EH EL34 power tubes that came with the amp?

How many hours are on the tubes? Average life is about 2000 hours for a power tube.



Setup and use

Setup doesn’t get much easier, especially for a tube amp. After input, speaker, and power cables are connected, it’s simply a matter of flipping the power switch and checking the negative bias setting on the output tubes. This is pretty simple too, accomplished by inserting the probe from a standard voltmeter into a spring-loaded socket adjacent to each tube. Yes, it’s a little more work than biasing an amp that has one test point for all the output tubes, but it offers one key advantage -- as the tubes are individually biased, the need for a perfectly matched quad of tubes is nonexistent. Manley indicates at least several years of life can be expected from the output tubes, as they are run at fairly conservative voltages.

The factory-recommended negative bias voltage is 300 millivolts per tube, and while I noticed some small drift during the first 100 hours of operation, beyond that point bias remained rock-stable. According to Manley’s chief, EveAnna Manley, 300 millivolts is the setting that offers the best operating point for the EL34s in this push-pull, ultralinear circuit, and she does not recommend altering this setting. So, being a good boy, I set the tubes accordingly, and all review comments below were with the amps locked into this bias voltage. A few other words of advice, warning, or whatever you might wish to call them: (1) do not apply power to the amp without a speaker load connected, and (2) assure that the negative speaker lead is hooked only to a speaker post, not to an earth ground. Doing otherwise may cause a very short life for the output transformers, and a trip back to Chino, CA for repairs at your expense. Like most manufacturers, Manley does not offer warranty coverage for misuse or general stupidity.
[/I]
 http://www.soundstage.com/revequip/manley_snapper.htm

[G Georgopoulos]

deleted

[mick wolfe]

As jea48 has hinted, best run those Snappers with EH6CA7's. The Snappers put a fairly high voltage on the plates and the EH6CA7 is rugged enough to deal with it. Perhaps other 6CA7's will work as well, but I would definitely stay with a pure fat bottle 6CA7.

[Pryso]

Thanks all for your help to get me sorted out.

From what I know of Manley's history with the Snappers, when they were introduced they were delivered with EL34s.  However, problems with quality caused them to switch to 6CA7s for a few years.  I'm the second owner of my pair and from what I was told, they were delivered with 6CA7s.  Recent conversation with Manley tells me they are now back to EL34s with no reliability issues.  So it depends on the age of the Snappers for which tubes were supplied at the factory.

By moving the outputs from one amp which biases normally to the other amp and then substituting one tube (originally in that amp) at a time I was able to identify a tube which caused erratic bias readings.  So now hopefully with replacement of that tube and all should be well.

[jea48]

Thanks all for your help to get me sorted out.

From what I know of Manley's history with the Snappers, when they were introduced they were delivered with EL34s.  However, problems with quality caused them to switch to 6CA7s for a few years.  I'm the second owner of my pair and from what I was told, they were delivered with 6CA7s.  Recent conversation with Manley tells me they are now back to EL34s with no reliability issues.  So it depends on the age of the Snappers for which tubes were supplied at the factory.

By moving the outputs from one amp which biases normally to the other amp and then substituting one tube (originally in that amp) at a time I was able to identify a tube which caused erratic bias readings.  So now hopefully with replacement of that tube and all should be well.

So now hopefully with replacement of that tube and all should be well.

Should... I have never owned a Manley amp so I am not familiar with their Push Pull circuitry for their amps. Even though each power tube has its' own individual bias pot, for setting the bias voltage for each tube, I would still think the 4 power tubes would/should be matched. How does the oddball tube you stuck in get along with the other 3 power tubes in game of push pull? Is the oddball tube weaker than the other 3? How much life does the tube you stuck in have left? What protection does the circuitry of the amp have in the event a power tube shorts out? Is the oddball tube made by the same manufacture as the other 3?

Should.....

If it were my amp I would contact Manley tech support and get their opinion on what you have done.

New stock power tubes are cheap compared to a repair bill.

http://www.thetubestore.com/Tubes/EL34-6CA7-Tube-Types

[richidoo]

Erratic bias is usually (always?) the tubes fault. I used a lot of different tubes in Snappers and some were solid bias, others unstable. I've found New Sensor and Svetlana (SED) were very stable. Chinese and JJ not so much.

Mitch Margoles, the designer of the Manley Snapper, was also involved in the design of the Groove Tubes reissue of the GE E34Ls tube. This tube is was so awesome, Manley decided to build an amp around it. A very clever, fully balanced amp, with incredible custom designed, custom iron wound in house. The GT E34Ls tubes used original tooling and leftover filament materials from GE. Some improvement were made which boosted power a bit. They are a true 35W tube. Parts were shipped to JJ who was the contract mfg. The first batches of tubes were excellent quality and the performance was great for a few years. But as typical with JJ, eventually it goes to crap and this happened around 2007 when a bad batch went out. I bought a replacement octet from Manley and 4 of 8 blew up, damaging the amps, etc. Manley tried very hard to filter out the bad tubes, even building a new test rig, but the bombs still got through, so they switched to Electro Harmonix 6CA7 as the factory issued tube for new Snappers. Since my batch of GTs were such a disaster, Manley sent me a whole new octet of 6CA7s for free, a fine gesture. But the sound wasn't even close. In the Snapper, 6CA7 sounded blurred and boring compared to the GT E34Ls. GT still sells that tube (as does JJ) and maybe newer batches have been improved, maybe Manley is using it again? Note it is "E34Ls," not EL34.

I tried a lot of tubes to replace the EH6CA7s before I sold the Snappers, but nothing available then (2008) made them play like GT tubes. Black Treasure had just appeared, but I wasn't willing to gamble that much money for 8. Now we have Gold Lion, both of those should be very nice, much better than EH. I don't know if any tube would give the crisp cutting edge, strong bass and intense musical presence of the GT tubes. A phone call to Manley or Groove Tubes should prove interesting if you want to know current E34Ls status.

[jea48]

Deleted.

[Pryso]

richidoo, I appreciate your more complete story and sharing your experiences which added details to the summary I was told.  That all fits and makes sense.

I'm the second owner of these Snappers and all the EH 6CA7s had the same date code when I got them.  Over the first year I owned them there was one tube failure but that was taken out by a bad resistor.  Since the EH all tested strong and I have been pleased with the sonics of the amps, my intent has been to use the EH 6CA7s until they need replacement, then consult with Manley on recommended re-tubing. 

[Pryso]

I think (fingers crossed) all is finally resolved.  So for anyone else with Manleys or just curious about such a problem, here is what I learned.

Once I identified one tube which caused the erratic bias readings (which then occurred on all outputs with that amp), I thought I had the problem solved -- but I did not.  As it turned out, I had two original 6CA7s which caused erratic biasing, that complicated the tube switching process in testing.  In addition, the one spare (new) EH 6CA7 I had on hand could not be biased lower than around 500 mV.  The Snapper calls for 300 mV.  So I was dealing with three bad tubes, all at the same time.  Patience won out, I've ordered new replacements and am temporarily using two spare tubes marked EL34/6CS7.  At least they bias and the amp sounds OK.