New Amp Build, What Options do I have?

[GuitarZombie]

Hey,
I picked up an old tube Sherwood s-3000 Fm tuner for dirt cheap. Still packed with tubes and all. Thinking of using it as a platform to build.
Here's some info:
Tubes :12at7, 9 pin, .15A
6ab4, 7 pin, .15A
6bs8, 9 pin, .4A
6br5, 9 pin, .3A
6bn8, 9 pin, .3A
4x 6au6, 7 pin, .3A
6x4, 7 pin, .6A
10 Tubes total, four noval sockets, six minature sockets, power transformer able to supply 2.5A draw plus .6A for rectifier, and a chassis.

So, what options on builds would anyone suggest? And in turn, what do I need to look for Output transformer-wise with your suggested build? I'm not limiting myself to these tubes themselves, just listed them for their current draw and sockets. Though I know there are some amps out there with 6x4's as rects.

I was thinking something Vox-like. Ac15-ish. Like 2 xel84's (there's two of the novals), 6x4 rect, and 2 x12ax7's (the other 2 novals), and maybe fill in if needed with some 6av6's? 6ab4's? 6c4's? Use the minatures for driving verb or trem or something.

Would a 6x4 be fit with 2x eL84'S?

I know I could dumb it down and just use the four novals with two 12ax7's, two el84's and ss rect. Or one 12ax7, two el84's and noval rect. two 12ax7's, one el84, noval rect.........

Any suggestuions?

[GuitarZombie]

suggestions. (sic)

[eschertron]

What's the voltage of the PT HV secondary? Is the 2.5A rating on this or the primary side? (2.5 * 120vac pri would still be 300VA, roughly 300 watts. In a tuner?)

[bob p]

tuners have line level outputs, not speaker level outputs, so i doubt that you're going to have much luck building an amp out of it -- unless you wanted to go with one of the really low-powered amps that run preamp tubes in push-pull arrangements.

[Enzo]

I think his 2.5A was the total the existing tube heaters drew, so he inferred the transformer could provide at least 2.5A on the 6.3c secondary.

If we look at it as a chassis with sockets and a power tranny, you could probably do something, but it would be small in power. The amount of current in the high voltage would be telling.

[GuitarZombie]

Bob, I'm planning on getting a proper OT after deciding on what to build. Would like something 15 watts, but won't rule out 5-10 watters. Looks like Skylarks run a 12ax7, el84 and 6x4. Something like that, but maybe use some more of the sockets because thay're there.

[bob p]

as others have noted, the real question about building the kind of amp you've been talking about is whether or not your PT is up to the task of running EL84. for a tuner PT, i doubt it. i'm thinking that your tuner PT might be good for building a moonlight or a firefly, though.

[GuitarZombie]

I don't follow. Why would it have trouble with an el84? Not enough voltage?

[bob p]

1. you might not have enough current sourcing capability in the HiV secondary of your PT.
2. even if you did, that PT is designed for supplying preamp tubes, which would mean that it's designed to produce low voltage. that voltage may/may not be suitable for good tone with the power tubes you want.

[GuitarZombie]

gotcha. So a voltage reading would give us some idea. At the plates of various tubes?

[Enzo]

Look at it this way, any car can drive down the highway at 70mph, even a little Yugo. But only the more powerful ones can drive that fast while pulling a heavy trailer. And that is the difference here too. The tuner circuits are all low current circuits equivalent to a preamp, none of them need any current to speak of, but a power amp does need current. The question here is whether the existing power transformer can provide high voltage at enough current to satisfy power tubes. VOltage is not the real issue.

Maybe a better analogy is flashlight batteries. There are the tiny AAA cells like in a TV remote, and then there are the big D cells like in large flashlights or other things. Both are 1.5 volts, but the D cell has much greater current capacity.


Not saying yours won't work, it is just an important consideration to look into.


If you have not yet torn it apart and it is more or less intact and can be powered up, then do power it up and break into the high voltage supply to measure the amount of current being drawn from it. I am sure there was extra margin there, but we'd at least know what the thing was expecting as a load.

[GuitarZombie]

Ok. Thanks for dumbing it down for me. Still picking up on this stuff as I go.

Haven't torn it apart yet so I'll power it up and take some measurments.

If a no-go with the power tubes, maybe something like a Herzhog!?

[Joe L]

I think this video is appropriate.

[bob p]

> video

i'd like to see the video where his wife kicks his ass for ruining up her formal dining room table.