Has anyone built this battery tube amp?

[Puguglybonehead]

OK, not a pedal topic. (not sure if I should ask on a tube amp forum or something) I've look over the schematic linked at the bottom of this page numerous times: 

https://www.ampbooks.com/mobile/amp-technology/battery-amp/ 

Richard Kuehnel describes how you would go about making a battery powered, push-pull guitar amp using old beach-radio tubes. 1T4 and 3S4 types. I've gone as far as buying a number of both types of tubes and even found an output transistor to fit the bill. I just can't seem to wrap my brain around the actual wiring. It gets especially confusing when looking at how the 3 power supplies required are hooked up to each other.

https://www.ampbooks.com/mobile/amp-technology/battery-amp/battery-amp.gif

Has anybody else out there attempted this build or anything similar with these types of tubes? I realize it probably won't be very loud, even with an efficient speaker, but I'm intrigued with the concept of using tubes that were meant for beach radios. A beach amp.

[GGBB]

The battery connections do look a bit strange - the "SW" threw me at first - but it's actually simple - this should help I hope:



Then connect all A+ together, B+ together, and C- together.

[Puguglybonehead]

Thanks. That does make it much easier to picture. The grid supply (C-) is definitely what threw me the most.

[GGBB]

Curious - what do you plan to use for the 45V battery?

[Puguglybonehead]

For the time being, I'll just try five 9V batteries in series. There are some decent rechargeable 48V Li-ion options out there now though, due to the popularity of E-bikes. I won't decide on what to do cabinet-wise until the B+ solution is figured out. Also not sure which speaker to use. I have one of these 8" speakers around: https://qcomponents.ca/collections/guitar-speakers/products/riftone-g825m-8-ohm-guitar-speaker but I'm tempted to use something louder like a 10" Eminence Ramrod, but the extra expense (and weight) probably isn't worth it for only a 3db improvement.

[PRR]

FWIW, "all" beach radios I have seen switched both the A and B batteries. (And very few used a C battery, though battery home radios did.) Here the common 390r resistor R10 back-biases all stages.



For initial smoke-tests, 12V of B+ is plenty. That was often done on DIY camp radios, where cheap reception beat party loudness.

[amptramp]

The 3S4 output tubes could be replaced by 3Q4 which is actually rated for -4.5 volts on the grid.  The 3S4 is rated for -7 volts on the grid.  For real performance (I hope the sarcasm is getting through), use 3Q5 octal tubes for more power and gain.

A couple of green LED's in the B battery return line could provide the negative C bias for the stages that need it.  As PRR showed, all my beach battery sets use a resistor to get a negative bias voltage.

[Puguglybonehead]

I'll stick with it as drawn for now. I'm wondering about the OT impedance. It's hard to find anything that exactly matches the required 10K primary. (without spending more $ than this is worth) I can come sort of close with a Hammond 125A. Am I better to err on the high side or the low side with matching the primary impedance?

[PRR]

"Matching" is for Maximum Power (or something).

Starting with a 45V supply and the smallest things we call "power" tubes, I don't think you are really seeking POWER.

Use what you can get.

I recently saw a 0.1 milliWatt audio amp called "audible".

[Puguglybonehead]

OK, sorry to bring this topic up again. I'm finally just about to start gathering the parts for this. Had a bit of a pest control problem in our building to deal with here that set everything back by months. Grrrr. Anyways, looking at the schematic, having never built a tube amp before, what does the "G1" connection that appears twice on the drawing refer to? Is this another ground point? Or am I just connecting these two together?

[PRR]

" I just connecting these two together?"

This.

[Steben]

Check these tubes:

12U7
12K5

[Puguglybonehead]

Check these tubes:

12U7
12K5

I've already got 'em. Stephan's 12K5 project from his Sopht Amps website is yet another thing on my pending build list. I started building the final version of his 12V 12K5 but put it away in storage due to life interruptions. Got as far as punching holes and placing all the tube sockets and the O.T. in a small chassis but I haven't gotten around to wiring it up yet. (gotta find the switching adaptor I put away for it as well) Hmm....This might be just the thing to do before working on the 1T4/3S4 amp. Curious to see how loud 35 mW will be through the 15" Eminence I've got sitting around here.