Fender 6G15 Reverb unit, why use a 6K6 (6V6) instead of the usual 12AT7 ?

[Iplayloud]

I have been considering building a Reverb Unit lately and I already have most components except for the special reverb transformer.
The usual unit from vintage Fender style amps are not the right specs. I can't help but wonder why not use a 12AT7 and use a usual reverb transformer.
I already have one spare on the shelf so I was hoping to avoid having to order a special one...

[Iplayloud]

Honestly I have never actually used a 6G15 unit, of course the 6K6 has more power and will probably drive the pan harder but I always felt the 12AT7 in a AB763 style circuit was more than enough to get the tank knocking it's head off!?!
Oh and by the I didn't post in the effects section because thet are mostly opamp people I believe.. while this unit is tube amplification guitar stuff..

[Enzo]

Effects are effects, even if they run on steam and eat coal. Most of those guys are into small solid state because that is what most effects are made of.

If you want to use a 12AT7 and "regular" transformer, go ahead.

[Iplayloud]

Sorry I didn't want to piss anyone off, or imply that the effects people are any less competent or knowledgeable.

[Enzo]

Oh, no one is pissed off or anything. I was just pointing out that while you may be right that most of the guys in that section are into op amps, that doesn't make this an amplifier, it is still an effect. No big deal, it is a perfectly good question to ask.

[Iplayloud]

It's rather unfortunate because they have nothing to say about it over there, I was hoping to get recommendations about what cathode resistor to use with an EL84 and, grid, screen resistor values. I will probably copy the values of the Vibro King (Rev.A) but it has only one gain stage before the power tube so I'm not sure if all values can apply.. This is really tube amp stuff, except the speaker is a reverb transducer

[Enzo]

Well, honest, we are the same guys mostly. I don't really have anything worthwhile to contrinbute to this. To me, the drive is just a little power amp, nothing special. SO to me it is build whatever you like at that stage. This is a guitar amp not a NASA space probe. There is no precision circuitry here. You have a reasonable B+ for any tube you would chose, the demands on it are not large. And the fact that you already know of all these various circuits to drive the same reverb pan tells you it is very flexible.

[loudthud]

You could use a 6BM8/ECL82 tube. A small power power tube and triode in a 9 pin bottle.

[Chuck H]

+1
You could almost certainly get good performance from a single tube. If it's the right one for the job, like the 6BM8.

FWIW, I've had good success driving reverb pans with a single 12au7 triode. In fact a lot of people have. The only rub is the input signal voltage will clip the driver at higher gain settings unless you attenuate it. And then you get a little less BOIIING! effect at lower signal levels. Still a perfectly respectable reverb. But I think THIS may be at the heart of why the Fender stand alone reverb uses a bigger power tube. I haven't researched it, but I'd wager there's more headroom WRT input voltage with the 6K6. Not to mention the added benefit of a slightly larger OT which MAY have better audio properties. But I'm just speculating now. With an inference that there IS a legit reason Fender designed that box the way they did.

[kleuck]

You could use a 6BM8/ECL82 tube. A small power power tube and triode in a 9 pin bottle.

You can do a lot of things with a 6BM8 (and a fet here)



http://youtu.be/4GyagcosWe4

[Chuck H]

Tre' nano!

[Gingertube]

Many folk like ECL86 as well (6GW8), same concept, it is a 12AX7'ish triode and a 6M5 (EL80)'ish power output pentode in a single package.

So any off:
ECL82 (6BM8) - triode is 12AT7'ish, readily available, recommended
ECL84 (6DX8) - excellent russian equivalents available, new production, recommended, I prefer them to the 6BM8
ECL86 (6GW8) - the best triode/pentode ever made but not in modern production
ECL85 (6GV8) - there are a S..t load of these floating around (NOS) and used - used in TV sets, no modern production. An overlooked tube.

There are also:
ECL80 - I have seen exactly one of these ever!!
ECL81 - I assume, never seen one.
ECL83 - Used a lot in cheap late 60's record players. Again I think they have been all used, no prodern production.

The 6G15 Reverb sound is superior and I think that has to do with better drive of the pan.

OR
You can say "It's and effect" so it doesn't need to be tube and drive it with an opamp BUT note that most of the amps with a reputation for crap reverb use op amp drive, most of the amps with a reputation for decent reverb use tube drive.

I use either push pull 12AT7 (A Kevin O'Connor rip off) or single ended ECL86. If I were to build a 6G15 stand alone reverb I would use SE 6V6 and 6SL7 for recovery.

Cheers,
Ian

[soundmasterg]

Many folk like ECL86 as well (6GW8), same concept, it is a 12AX7'ish triode and a 6M5 (EL80)'ish power output pentode in a single package.

So any off:
ECL82 (6BM8) - triode is 12AT7'ish, readily available, recommended
ECL84 (6DX8) - excellent russian equivalents available, new production, recommended, I prefer them to the 6BM8
ECL86 (6GW8) - the best triode/pentode ever made but not in modern production
ECL85 (6GV8) - there are a S..t load of these floating around (NOS) and used - used in TV sets, no modern production. An overlooked tube.

There are also:
ECL80 - I have seen exactly one of these ever!!
ECL81 - I assume, never seen one.
ECL83 - Used a lot in cheap late 60's record players. Again I think they have been all used, no prodern production.

The 6G15 Reverb sound is superior and I think that has to do with better drive of the pan.

OR
You can say "It's and effect" so it doesn't need to be tube and drive it with an opamp BUT note that most of the amps with a reputation for crap reverb use op amp drive, most of the amps with a reputation for decent reverb use tube drive.

I use either push pull 12AT7 (A Kevin O'Connor rip off) or single ended ECL86. If I were to build a 6G15 stand alone reverb I would use SE 6V6 and 6SL7 for recovery.

Cheers,
Ian

Ian,

When you use the push-pull reverb ala KOC, what do you use for the transformer? I was thinking about trying this myself....

Greg

[Gingertube]

Greg,
I bought it from Kevin himself
REV - LP Style Reverb Loop Kit

Knowing Kevin the tranny will be an off the shelf Hammond Unit
I have a vague recollection of it being a 109L from this range Hammond Mfg. - Miniature Epoxy Potted Audio Transformers - (107 - 109 Series)
It is a 10K to 3.2 Ohms which would reflect a 20K Raa with an 8 Ohm pan connected.

Here is a picture during build, the tranny is the small black thing RHS, pic is not high enough res for me to zoom in and read the type number but it definitely Hammond.


Cheers,
Ian

[kleuck]

ECL84 (6DX8) - excellent russian equivalents available, new production, recommended, I prefer them to the 6BM8

Interesting, can you explain why ? Only in reverb usage or for small amps too ? Power is lower than with ECL82/6BM8/6F3P.