Benson - Vinny 1 Watt amp

[unknowntome]

Hello .. stumbled across some of these internal Benson Vinny pics that I thought some of you might be interested in. Looks like it could be a fun small build!!

From the website:

1 x JJ EL84 power tube, 1 x JJ 12AX7 preamp tube

1 watt into 8 ohms

Post-output-transformer preamp level output

Built in load resistor for silent direct operation

[Stevem]

If you have a Fender amp with a tube driven reverb circuit ( 12AT7 ) just unhook the cable going to the input of the pan, and hook up a 8 ohm speaker and then you have yourself a 1 watt single ended amp.

[unknowntome]

If you have a Fender amp with a tube driven reverb circuit ( 12AT7 ) just unhook the cable going to the input of the pan, and hook up a 8 ohm speaker and then you have yourself a 1 watt single ended amp.

Wow… awesome idea! I’ll keep that in mind!

[unknowntome]

Just realised that a schematic does exist within the Benson Monarch thread and is imbedded in the Dizzy Bird schematic which combines the Vinny with a reverb circuit.

[unknowntome]

So I've just done my best to put together a layout using the schematic in the previous post.. please go easy..this is my first attempt at a layout!!

I used DIY layout creator.

Edit: 5/8/22 edited layout.. this layout is a combination of the schematic in the previous post as well as what ive managed to glean from the photos. I pretty certain its accurate however yet to be verified. UNVERIFIED for now.

[unknowntome]

Also, not sure exactly what type of transformers are being used with this circuit.

This is the only image I could find online identifying the power (?) transformer.

[unknowntome]

Tuning in to see if anyone has any ideas what type of transformers would be suitable for the Vinny.. ? Looks like a fantastic project!

[Phil_S]

Really, not enough information to say with any certainty. If there were voltages on that schematic, it would tell us the answer. Your typical EL84 single ended amp will be a 4-5W amp using a PT that's something between 225-0-225 and 275-0-275, depending on the rectifier. Reducing to 1W suggests a much lower high voltage secondary, I guess something between 100-0-100 and 175-0-175. I don't want to guess at current draw. You might have some luck trying to model this in Duncan's PSU, but it would still require several guesses. I think this is why no one here wants to bite - not enough information, too many guesses to make.

Is there something special about building this amp? There are other, easily accessible, fully documented 1W amps. I suggest looking for and choosing one of those.

[unknowntome]

Really, not enough information to say with any certainty. If there were voltages on that schematic, it would tell us the answer. Your typical EL84 single ended amp will be a 4-5W amp using a PT that's something between 225-0-225 and 275-0-275, depending on the rectifier. Reducing to 1W suggests a much lower high voltage secondary, I guess something between 100-0-100 and 175-0-175. I don't want to guess at current draw. You might have some luck trying to model this in Duncan's PSU, but it would still require several guesses. I think this is why no one here wants to bite - not enough information, too many guesses to make.

Is there something special about building this amp? There are other, easily accessible, fully documented 1W amps. I suggest looking for and choosing one of those.

Hey Phil! Thanks for your thoughts.. I've played this amp a heap of times and it really does sound incredible.. much like a lot of the YouTube clips online... having said that, I haven't played through any other 1 watt amps before so can't compare.

I done have much more info to share.. some basic research leads me towards a 1750A or 125ASE output transformer. ... Not sure exactly which power transformer would be 'most' appropriate.. the image I posted above in a previous post is the closest thing to identifying exactly what it might be.

[Phil_S]

It's not clear. Do you actually have that amp or access to that amp? If you do, you'll need to get voltage readings from it. Then you can buy something similar. Otherwise, you will need to track down the manufacturer to get the spec. The numbers on the PT don't follow any convention I know. It looks like that PT was made in the Philippines, so good luck with that. Well, I realized, the Vinny was made in Portland, OR, so you might track down whoever made the amp and ask.

[Stevem]

If you built that with a 6BM8 which is like a lesser wattage EL84 and a triode in the same bottle you could have the second triode section of that first preamp tube free to use as a added gain stage.

[Phil_S]

I don't know if I have the right idea. I'm thinking the way to make a 1W amp with what is typically a 3.5W or 5W tube is to make plate and screen to around 125V. From there, assuming solid state rectifier, the PT needs a high voltage secondary of about 85-0-85 or 90-0-90. 35-40mA capacity should be more than enough. Does this seem right? A PT is a PT. I'm thinking brand and exact spec for the OP's question aren't all that important.

Good idea on the 6BM8!

[unknowntome]

I don't know if I have the right idea. I'm thinking the way to make a 1W amp with what is typically a 3.5W or 5W tube is to make plate and screen to around 125V. From there, assuming solid state rectifier, the PT needs a high voltage secondary of about 85-0-85 or 90-0-90. 35-40mA capacity should be more than enough. Does this seem right? A PT is a PT. I'm thinking brand and exact spec for the OP's question aren't all that important.

Good idea on the 6BM8!

Thanks Phil.. I’ve been looking around for something in that ball park with a 240v primary (located in Australia).. without luck. Having said that, my tube amp building is just beginning so chances are I’ve overlooked an obvious option… and yes, your assumption about the solid state rectifier is correct.

Edit: I’m wondering whether a reverb PT is more in the ball park… Hammond 290Wex? (along with the hammond 1750A OT).

[Phil_S]

Honestly, I don't know why I keep responding because there isn't enough information to get what you want. Having said that, you can build something that isn't too far from what you describe, however, you shouldn't think about comparing it. Maybe you can get a Hammond 369AX and 125ASE or 125BSE universal single ended output. The transformers you reference seem all wrong; high voltage secondary is too high and the reverb transformer has a primary that matches better to a 12AU7 used as the power tube.

[unknowntome]

Thanks for your insights yet again Phil

I’m still very much in the beginners realm of amp building which explains my fumbled attempts at trying to find the right transformers. I’ve just successfully built the Benson Monarch which was an amazing accomplishment especially since I chose to make it rather unconventionally..(attached) .. it’s dead silent and sounds fabulous! The Vinny build was to compliment the monarch, and in reality, will be my only builds for a long while.. how many amps can one person build/own?! .. perhaps I shouldn’t ask that here! Plus, I really loved the Vinny when I had the chance to play it.

I’ll consider your helpful suggestions and hopefully some more info might come to light!
Cheers!