Amp/ tube gurus, help!!

tele4tone · May 8, 2009

So I bought one of these amps from a recommendation of an out of state friend.http://www.myspace.com/classof57amps

He stated that this amp was around 15-20 watts. It is based on a '57 princeton circuit. I asked for a 6L6 tube in the output. I received the amp yesterday and it plays well, but it is nowhere near 15-20 watt output to my ears. It was about equal to my valve jr (which I love) played with the same cabinet.

I checked the output tube and it is a 6K6. I think those are older versions of a 6V6? The preamp tube is a no name. I guess 12AX7.

How much more output can I get with a 6L6/KT66 or a EL34. I have a 1-12 cabinet and a 4-12 cabinet.

Help. Suggestions? I may return it. I already have two low power amps.

Walter Broes · May 8, 2009

a 6K6 is a lower output version of a 6V6, so yes, a 6L6 tube would get you more than twice the output, even in a single-ended configuration I think.

Question is if your amp's transformers are designed to deal with bigger tubes...?

JonL · May 8, 2009

15 to 20W is impossible in that circuit, no matter what tube you use. The maximum rated output of the tubes you mentioned when used in a single ended amplifier like yours are:
6K6: 4.5W
6V6: 5.5W
6L6: 10.8W

An amp builder might be able to squeeze a little more out of the tubes by exceeding their maximum ratings, but it would shorten tube life and be very risky with new production tubes that aren't typically as rugged as the old stuff.

You *might* be able to get more power or headroom by switching from a 6K6 to a 6V6 or 6L6, but it will depend a lot on other factors in the amp, including the transformer.

A single ended 6V6 amp can get pretty loud if it's paired with an efficient speaker. Loud enough to do rehearsals with a quiet-ish band, especially the drummer's gotta lay back.

capnjuan · May 8, 2009

Walter Broes said:
a 6K6 is a lower output version of a 6V6, so yes, a 6L6 tube would get you more than twice the output, even in a single-ended configuration I think. Question is if your amp's transformers are designed to deal with bigger tubes...?

Hi Tele4tone; Walter is correct in both respects; yes - any of a 6L6 / KT66 / EL34 will increase the power output but the question is whether the power and output transformers and the power supply will support anything else. The 6L6 and KT66 share the same pinouts but the EL34 doesn't. Finally, any combination of power and output transformers optimized for a 6K6 or 6V6 will not support a single 6L6 ... see JonL's post above. My suggestion would be to Take It Back ...

:wink:

tele4tone · May 8, 2009

My buddy has had one for a year and primarily uses a 6l6. He is a gigging musician so it is used alot. He has not had any problems yet

This is the info that the amp builder posts.

INFO: For CLASS OF '57 AMPS

.. ..

1. Hand built point to point.
2. New Old Stock (NOS) 50's carbon resistors throughout / higher watts than most amps today.
3. All amps equipped with genuine 50's tubes until we are out.
4. Class A with cathode bias.
5. Amps are engineered to give you power to drive a modest 10' speaker or a Marshall stack depending on how much air you need to push.
6. Class of '57 heads uses paper wound output transformers exclusively.
7. Heads designed to give tweed sustain and compression with black face punch and head room.
8. Convertible design allows you to customize your tone with exchanges in both tube positions with out need to rebias the amp.

.. ..

Preamp Gain Output....

12AX7 100 6V6

12AT7 60 6L6

12AY7 40 EL34

12AU7 17 7408

7025 100 5992

6201 60 5881

6072 40 5932

5814 17 6CA7

6681 100 7581

6679 60 KT-66

6680 17 KT-77

5751 70 5871

12BH7 16 1622

12BZ7 100 Absolutely No 6550's or KT-88's

.. ..

9. Rectifier Parameters:
1. All heads come with diode rectifiers. You can use tube or solid state rectifiers.
2. Approved tube rectifiers: 5AR4, 5V4GA, 6106, GZ-30, GZ-32, GZ-34, 5R4 and 5Y3. Absolutely NO 5AU4's, 5U4's, OR 5V3's.
3. Remember – diode rectifiers suck no power out of the power transformer. Tube rectifie

[/quote]

The transformers are not huge I could probably get some info off of them tonight. Thanks for all of the info fella's.

capnjuan · May 8, 2009

Hi tele4tone: One the wall in the men's rooms at the rest stations on the FL Turnpike, they have these vending machines ... you know what kind of vending machines I'm talking about and they all say: "One size fits all" ... it isn't true for what they're selling, men's socks, and it isn't true for output tubes unless your seller can produce some engineering data about how he has that covered. Charming idea but ... Best wishes, John

JonL · May 8, 2009

They might be good sounding amps. You can certainly get a wide range of tonal voicings by trying all those different tubes. As the previous poster said though, the circuit can't be optimized for all those output tubes. It may "work," in that it makes sound, but its unlikely to be as good as an amp that's designed to use a narrower range of output tube types.

The gain column is simply the amplification factor for the corresponding preamp tube. It really doesn't have anything to do with the power the amp can produce. I don't know why he has the power tubes listed in an adjacent column, it implies that the listed power tubes have to be used with the corresponding preamp tubes (and vice versa) which I'm sure isn't the case.

Regardless of the versatility it'll never be more than about 10W max, and probably less. 10W can be plenty loud with the right speaker, but it still may not be enough for what you want.

I don't know why he sent you a 6K6 when you asked for a 6L6... maybe have him send you a 6L6 to try before you decide if you want to return it.

tele4tone · May 9, 2009

I dropped an old tungsol 6v6 in and it already sounds better. Gonna order a 6l6 and see what happens. For the record my friend stated the 15-20 watts, not the amp builder. He states 10 watts.... I can live with that. I'll update soon..... LTG rocks! Jeff

capnjuan · May 10, 2009

Hi Jeff; 10 watts is about right. Good luck! J

tele4tone · May 18, 2009

So I got an old rca 6l6 and slapped it in there. umm :? . My tungsol 6v6 sounded way better and the output wasn't really noticeably louder by my ears. Crap....... I'm sending it back. This thing sounds great, but I already have two other low wattage amps. Thanks for all the help fella's!

JonL · May 18, 2009

Are you certain the 6L6 is good? RCA blackplates have gotten so expensive that there are many, many used tubes being sold as "good" that should be in the trash. I wouldn't expect the 6L6 to be louder, but I would expect it to have a more masculine character - tight and beefy in the low end, clear and articulate, and more headroom. Less drive and compression when cranked.

tele4tone · May 18, 2009

Description
This is a used 6L6 GA ST shape power tube, made by RCA. It has been tested at 103% as measured in percentage relative MICROMHOS on a Jackson 648A dynamic tester. Return tube if not fully satisfied.

That is what I bought on ebay. I tested it on my tube tester as well before I tried it in the amp and it came out good.

I agree with your description of the tone and liked the tube. It just didn't have enough power for my current band. This builder has another model that is class ab push pull. I may try that one because I loved the tone and the chassis and parts assembly was very nice.

JonL · May 18, 2009

Sounds like the push-pull amp is going to be more what you need. Much more power. I also think the overdrive sound of a single ended amp is great by itself or for recording but tends to get lost in the mix with a band unless the band has a very sparse, clean sound.

I've never tried an RCA 6L6GA, only the GC. IIRC, the GA is more like a 5881. I've got a couple of Tung Sol 6L6GAs laying around waiting for me to try. (Or maybe they're GBs... I don't remember.) I pulled them from a garage sale phonograph. I'm waiting until I have more time because I'll want to check the bias carefully on them. I think my old Vibrolux will put a lot of plate voltage on them and I don't want to fry them immediately.

Good luck with the new amp!

Amp/ tube gurus, help!!

tele4tone

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Walter Broes

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JonL

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capnjuan

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tele4tone

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