Single Power amps & tube adapters

[Elephas]

First, let me point out that I don't know much about amps and electronics.

I've been wondering about how Single Power amps use tube adapters. I have an ES-1 and several types of adapters which allow the use of a variety of tubes. The default configuration is 2x 6SN7 per channel in the two gain stages, for a total of four 6SN7, and then 2x EL34 power tubes per channel, for a total of four EL34 tubes in the amp.

Four 3D21A adapters allow the use of 3D21A tubes in place of the EL34. Two 2C51 adapters and two 5687 adapters allow the use of the respective tubes in the 6SN7 positions. Two "ECC-1" adapters also allow the use of 12AU7, 12AX7 and 5751 in the 6SN7 positions. From my communications with Mikhail and his recommendations, it appears that the adapters can be used in various combinations and in either the first or second gain stages.

I know some other tube amps can also use tube substitutes and adapters. For example, a local audio shop sells 12AX7 to 6SL7, 6CG7 to 6SN7, and 12AU7 to 6SN7 adapters and I bought four of each. They were very inexpensive.

I asked Craig about using a 12AX7 to 6SL7 adapter in my Zana Deux, and he explained that while it might be possible he doesn't recommend it because the 6C33C-S tubes are biased with the 6SL7 and might not work correctly with a 12AX7 in there. He says the 12AX7 is not an exact substitute for the 6SL7.

I'm aware that there are some direct tube substitutes, such as 7N7 for 6SN7 or some fairly close substitutes which may or may not work depending on the individual tube amp.

How is it that many Single Power tube amps can use a large variety of tube types utilizing the adapters? I've asked Mikhail about this and he says it is because of the special design and capabilities of SP amps.

The adapters themselves are sold by SP at very high cost. They are much more expensive than the adapters I bought locally. Is there anything special about the SP adapters, or are they basically the same as any other tube adapter?

[tagosaku]

I have both SP and GT adaptor for 12xx7 -> 6sn7. GT version is cheaper and has a better tube socket and I can not tell the difference...

[nikongod]

I know some other tube amps can also use tube substitutes and adapters. For example, a local audio shop sells 12AX7 to 6SL7, 6CG7 to 6SN7, and 12AU7 to 6SN7 adapters and I bought four of each. They were very inexpensive.

The 12ax7 to 6sl7 and 12au7 to 6sn7 adapters are likely the same. Return some if you can. If you have a multimeter, verify that none of the connections have resistors (they probably dont) and then your set.

He says the 12AX7 is not an exact substitute for the 6SL7.

Nope, not an exact swap.

12AT7 may be a close enough approximation to the 6sl7. Bonus round, it uses the same adapter as the others above.

OTOH, the ZD uses a bunch of global feedback, the funky capacatances of the adapter may interfere and cause "funk."

How is it that many Single Power tube amps can use a large variety of tube types utilizing the adapters? I've asked Mikhail about this and he says it is because of the special design and capabilities of SP amps.

Its a mater of riding on tolerances. Some combinations are downright weird and stressful with how they run the tubes. Others are simply making use of the same tube in a different bottle, or with different pins. some other options use big ass power tubes loafing along under very low loads.

The adapters themselves are sold by SP at very high cost. They are much more expensive than the adapters I bought locally. Is there anything special about the SP adapters, or are they basically the same as any other tube adapter?

ECC-1 wired straight through.

5687: has some extra resistance on the cathode of 1 section so they dont draw tooooo much current in the output stage. I dont know if there are "speshul" 5687 adapters for the ES-1 with resistors on BOTH cathodes or no resistors. Im also not aware of anyone but mikhail building this adapter.

Others: no idea you can tell in about 2 min with a multimeter and pin-out diagrams though.

[jp11801]

OTOH, the ZD uses a bunch of global feedback, the funky capacatances of the adapter may interfere and cause "funk."

Ari have you measured the global feedback used in the ZD? When I asked Craig about the above statement , previous made by Earl (I believe) Craig stated it uses very little global feedback?

Not trying to create a stink just wondering if you measured the GF or are going on previous statements made about the ZD.

Edited June 22, 2009 by jp11801

[nikongod]

Not trying to create a stink just wondering if you measured the GF or are going on previous statements made about the ZD.

Im going on previous statements.

[spritzer]

I've asked Mikhail about this and he says it is because of the special design and capabilities of SP amps.

Hahahaha... that just made my day. The bottom line is, in a circuit like the ES-1 is very easy to use different tubes. Now whether it is a good idea is debateable but I don't think it is a great idea to run some of these tubes on a +400v PSU. When I modified the circuit for the A11 I would only use ECC99's in the second stage due to their high voltage capability and it's only running at +350v. I stuck a ECC83 in the first stage to get the high gain but I've yet to try how it behaves at full power.

[Elephas]

I was wondering if the propensity for Single Power amps to break down is related to their "flexibility" with the tubes and adapters. If the tolerances are necessarily loose in order to accomodate the different tubes, might that also make the amp more susceptible to breakdowns?

As far as I know, SP amps are the only tube amps with so much flexibility with the adapters. If this isn't because of some special genius technology on Mikhail's part, maybe other tube amp manufacturers don't do this because it isn't a good idea?

Here's a look at my three pairs of SP adapters (except the 3D21A adapters not shown) along with the cheapo adapters, which cost me about US$9 each. I got a bunch of them because they're so cheap and now I don't know what to do with them.

[spritzer]

The different tubes used is certainly a part in the amps downfall. With the Extreme for instance there were some rather power hungry tubes used which when coupled with the crap build quality led to damage. The heater supplies were undersized and so were the HV lines.

Most manufacturers build and design their units to fit with one certain tube. All the operational parameters match said tube and the filament supply works just for it. Now that doesn't mean you can't put in some other tube to try. There are many close relatives with different pin configurations or slightly more/less gain etc. which should work just fine. On top of that you have the same basic tube design but with a different heater voltage. The ES-1 for instance was designed around the ECC81 and the 6CG7, both of which are easy to substitute for.

Some of those cheap adapters are identical to the SP units. My ES-1 lacks the ECC-1 unit so I checked and a 6CG7-6SN7 adapter is the same thing.

[morphsci]

On my ES-1 I no longer use the 2c51's and adaptors as I have had problems biasing the amp at times when I was using them. The 3D21 and 12Ax7 adapters seem to work fine.

[nikongod]

Some of those cheap adapters are identical to the SP units. My ES-1 lacks the ECC-1 unit so I checked and a 6CG7-6SN7 adapter is the same thing.

The pinouts are different.

The ECC-1 adapter is for 12a?7 tubes.

6cg7 had its own adapter.

[spritzer]

They have the same pinout, the 6CG7 and the ECC83, ECC99 etc. minus the heater CT.

I also had this saved, presumably from HF:

ECC adapter type 1

12CG7,

8CG7,

6CG7,

12AX7,

12AT7,

12AU7,

ECC99,

6414,

7062,

5965,

5963,

5814A,

5844,

ECC99,

PCC99,

ECC182,

PCC182

The full list might be in order:

Direct Plug-in

12SN7

8SN7

6SN7

6BX7

5687 adapter

5687,

7044,

ECC adapter type 1

12CG7,

8CG7,

6CG7,

12AX7,

12AT7,

12AU7,

ECC99,

6414,

7062,

5965,

5963,

5814A,

5844,

ECC99,

PCC99,

ECC182,

PCC182

ECC adapter type 2

6DJ8,

6922,

PCC88,

ECC88,

ECC189,

E88CC,

CCA,

6ES8,

9B

Loctal Adapter

14N7,

7N7,

7AF7,

7F7,

6350 (adapter),

6463

6456,

ECC99,

ECC182

2c51 adaptor

2C51

5670

Bendix 6385

WE 396A

[Elephas]

In my notes I have the SP ECC-2 adapter as being the one for:

6CG7

6GU7

6FQ7

12FQ7

I've never had problems biasing any of the front four tubes. The only times I've had problems were with EL34 quads that were not well-matched.

The shop also sells adapters the other way around, such as 6SN7 to 6CG7. I thought of getting a couple to use in a Stax SRM-T1W, but then I thought maybe the larger tubes wouldn't fit in the casing.

True, the SP adapters look better but they also cost a lot more.

[spritzer]

Ari is correct. Shame on me but I'm so used to connecting ECC83's up at 12.6v that I forgot about the CT's role...

As for using the 6SN7's instead of 6CG7, it should sound better due to the better voltage specs for some 6SN7's but you have to watch the filament current.

[Tachikoma]

So... all of the 6SN7 equivalents (7n7, 5692) will definitely work in the SRM-T1, right? What exactly did you mean by watching the filament current?

[kevin gilmore]

So... all of the 6SN7 equivalents (7n7, 5692) will definitely work in the SRM-T1, right? What exactly did you mean by watching the filament current?

Electrically maybe. Physically NOT A CHANCE. You would need an octal to 9 pin

adapter. (the reverse of what you think) You would have to punch holes

in the top of the chassis... Transformer will likely not have enough filament power.

[Tachikoma]

Aww, pity I found a 7n7 to 6CG7 adapter on ebay (Adapters 7N7 TO 6CG7 tubes amplifier SUB - eBay (item 250459037219 end time Sep-03-09 17:34:26 PDT)) and was interested in a swap.

[kevin gilmore]

Yep that is what you want. If you can get 2 of them, or 4 for the sr-007t and

don't mind running without the covers, then give it a whirl. I still think it

is a bad idea. 700 volts for a 6sn7 ??? Not a good thing.

[spritzer]

Do something more hardcore, a single 9pin plug to two 9 pin sockets with an external filament tap so that you can use 6S4A's in the T1.

[Tachikoma]

I can picture what that might look like Franken-T1 would be fun but it certainly isn't something I want to lug around too much.

I'm not very well versed in electronics, but from the spec sheets I don't see any difference in the 6CG7 and 6SN7's heater requirements (both use 6.3V 0.6A), and the 6SN7's voltage ratings look better if anything (450V max dc plate in class A vs 300V max for the 6CG7)

The spec sheets I'm refering to:

http://boozhoundlabs.com/howto/pdf/6SN7GT.pdf

www.cicognani.eu/pdf/Tubes/6cg7ge56.pdf

[mulveling]

I can picture what that might look like Franken-T1 would be fun but it certainly isn't something I want to lug around too much.

I'm not very well versed in electronics, but from the spec sheets I don't see any difference in the 6CG7 and 6SN7's heater requirements (both use 6.3V 0.6A), and the 6SN7's voltage ratings look better if anything (450V max dc plate in class A vs 300V max for the 6CG7)

The spec sheets I'm refering to:

http://boozhoundlabs.com/howto/pdf/6SN7GT.pdf

www.cicognani.eu/pdf/Tubes/6cg7ge56.pdf

Just to be clear - and I'm certainly nothing more than an interested tube novice by any stretch of the imagination - those specs are for the GTA/GTB version of the 6sn7, which is higher rated than the GT version. For audio purposes, there is no difference between the GTA and GTB. Nearly all of the "premium" vintage 6sn7 tubes are GT, and those are indeed rated at 300V (like 6CG7) with a lower plate dissipation than a GTB. So don't be sticking yer Tung-Sol round plates or Bad Boys in a circuit that calls for GTA/GTB! The other direction however, is perfectly fine - in fact I've gone that route for my new tube preamp since the GTB tubes tend to be far less microphonic, should last forever in that circuit, and good ones can be had for more reasonable prices (Sylvania tall-bottles, Tung-Sols, etc...).

[spritzer]

The heater current does appear to be the same so why not give it a try. Just measure the transformer temp to see if anything strange is going on. I do think that 6S4A's are the best option since they can take 500V easily...