Looking for Supro Thunderbolt 6420 Build info

[mikepukmel]

Awesome, thanks. Have you ever built or rewired an amp with a daisy chain ground scheme like this? For me, fear of a very large unknown.

[tubeswell]

Yes I have, and it works perfectly if you follow it.

[mikepukmel]

Getting dangerously close to major progress. New 9 pin sockets arrived. I have all the discrete components. I think I have enough wire to do the rough wiring on the board. The output transformer came in. Really cool frankenstein lab looking thing.

Last thing to figure out is the input jack wiring. I more or less understand the Fender type wiring now Shorting, and uses either one 68k or two in parallel for 34k (high low input). I have Cliff jacks, the same ones I bought for a JTM 45 build. But the Supro schematic does not show low/high and shorting. They *must* short unused inputs, no?

The Marshall and Fender (not surprisingly) wiring looks exactly the same. 1M grid leak, right on the input jacks, on the opposite side of the grid leak. The supro has the grid leak on the tube side of a small cap. I hope not to change the tone of the thing, but akk, its not 1966 and the components are not 1966 either. IS there something special about the placement and size 0.005uf/270k high pass filter on the input?

[Helmholtz]

Mishmash has grid-to-ground resistor missing. Grid needs a DC ground reference. I would use 1M.

[mikepukmel]

Mishmash has grid-to-ground resistor missing. Grid needs a DC ground reference. I would use 1M.

Thanks Helmholtz. I think I understand. The clip of the input jack wiring was copy/pasted from a JTM45 schematic. It has a 1Meg grid leak but does not have that odd capacitor between the V1 grid and input wiring. The Weatherford schematic (more authentic Supro) has a grid leak where its supposed to be.
So "grid leak" is a DC thing, so needs to be on the grid side of any capacitor.

In this case, can I move the 1M grid leak that is on the input jacks, and move it to the place the 270k is on the weatherford schem, will this work? I never quite understood, if the resistor is to function as a "grid leaK' why amp mfr's didn't put the resistor right there at the grid.

[Helmholtz]

In this case, can I move the 1M grid leak that is on the input jacks, and move it to the place the 270k is on the weatherford schem, will this work? I never quite understood, if the resistor is to function as a "grid leaK' why amp mfr's didn't put the resistor right there at the grid.

It doesn't matters where the grid leak R is physically located, but it needs to be directly connected to the grid to allow for DC current to ground.

It is not quite clear to me what kind of tonal changes you intend to achieve and what (switching?) input jacks you are going to use.
I prefer high (1M) input impedance, because this preserves the full tonal spectrum of the PUs. 270k input impedance acts like turning back the guitar's tone controls.
Now the Weatherford input circuit has a high pass filter formed by the 0.005µ (= 5nF) series coupling cap and the 270k grid leak. Its -3dB frequency is around 120Hz, so it cuts some bass. If you replace the 270k by 1M (this is what I would do), the -3dB frequency will be 32Hz. But if you like the 120Hz bass cut, you will need to use something like a 1.2nF coupling cap.

[mikepukmel]

It doesn't matters where the grid leak R is physically located, but it needs to be directly connected to the grid to allow for DC current to ground.

It is not quite clear to me what kind of tonal changes you intend to achieve and what (switching?) input jacks you are going to use.
I prefer high (1M) input impedance, because this preserves the full tonal spectrum of the PUs. 270k input impedance acts like turning back the guitar's tone controls.
Now the Weatherford input circuit has a high pass filter formed by the 0.005µ (= 5nF) series coupling cap and the 270k grid leak. Its -3dB frequency is around 120Hz, so it cuts some bass. If you replace the 270k by 1M (this is what I would do), the -3dB frequency will be 32Hz. But if you like the 120Hz bass cut, you will need to use something like a 1.2nF coupling cap.

Thanks. Well, Ive heard low resolution internet recordings of a few of the original amps, and id like to get as close as possible (which now I understand is sort of a ridiculous statement since the components, tubes and speaker are all new manufacture ) But anyway, close as possible.

I have switching cliff jacks, same ones used on a JTM 45 type build. Yeah, didn't quite understand that high pass, thanks, so it will be a little more "bassy" just switching out the 270k with 1M. I'll try that then order a 1.2N cap today, and see how that sounds as well.

The only reason for looking to switching jacks is that won't this amp let a bunch of noise in to through the unused jack wiring, when only one input is used, and the other (unused) jack is not shorting?

[mikepukmel]

Between 32hz and 120hz, that's the bottom 1/3rd of the guitar! So, the original amp would really cut the boomy bass quite a bit, before it even gets into the preamp. Hmmm.

82 Hz,
110 Hz,
147 Hz,
196 Hz,
247 Hz,
330 Hz.

[Helmholtz]

The only reason for looking to switching jacks is that won't this amp let a bunch of noise in to through the unused jack wiring, when only one input is used, and the other (unused) jack is not shorting?

You don't want the other jack shorting as this would place 2 x 47k across the main input. Leaving the unused input open won't increase noise with the main input. You will have noise if no input is used, though.

[Helmholtz]

82 Hz,
110 Hz,
147 Hz,
196 Hz,
247 Hz,
330 Hz.

That's only open strings. High register fundamentals extend up to 2kHz.

[soundmasterg]

If it was me I'd build the amp as original as possible, then once it works, tweak from there. The originals sound great and don't hum overly much. I've even used one in the studio for bass as it was originally intended and it sounded great, though we did use a 4x10 cabinet instead of the original 1x15. I plan to build my clone PTP as the original did, though it will be awhile until I get to it unfortunately. Would love to see pics and hear your impressions of it once you get yours done.

Greg

[mikepukmel]

If it was me I'd build the amp as original as possible, then once it works, tweak from there. The originals sound great and don't hum overly much. I've even used one in the studio for bass as it was originally intended and it sounded great, though we did use a 4x10 cabinet instead of the original 1x15. I plan to build my clone PTP as the original did, though it will be awhile until I get to it unfortunately. Would love to see pics and hear your impressions of it once you get yours done.

Greg

Thanks for the tip/suggestions Greg, what I have so far, is pretty close. Yeah, for me, its all about the tone! I started looking into ptp on terminal strips, but could not convince myself I could 'debug' it and get all the connections right, so I fiddled with some existing layouts on a board. Tried to mash the components close to the tube side of the board to keep wires short to the preamp and pi.

Only big item left is the PT, from Heyboer. Can't wait to hear the thing, will post photos, and try to find a way to get sound clips, as soon as its more 'together'.

[soundmasterg]

Thanks for the tip/suggestions Greg, what I have so far, is pretty close. Yeah, for me, its all about the tone! I started looking into ptp on terminal strips, but could not convince myself I could 'debug' it and get all the connections right, so I fiddled with some existing layouts on a board. Tried to mash the components close to the tube side of the board to keep wires short to the preamp and pi.

Only big item left is the PT, from Heyboer. Can't wait to hear the thing, will post photos, and try to find a way to get sound clips, as soon as its more 'together'.

Looking forward to hearing it and seeing pics!

You should try a PTP amp at some point. Draw it up on paper first and it will make more sense. Once you've done it, then it is easy to do more. The debugging can sometimes be an issue....I had one I built up out of an old Bogen, and it worked perfectly except once you got past a certain point on the volume control it would squeal. I couldn't find it on a scope, but by poking around with a chopstick I could make the noise come and go if I moved one wire. So I found where it was quiet and zip tied the wire in that spot. 4 years later the amp works flawlessly. Moral is, PTP sometimes takes a little more effort to sort out, but once you have it sorted, it won't change, and it isn't that hard to follow the circuit and troubleshoot it either.

Greg

[mikepukmel]

Greg, thanks, man will do! I think I'll try to find a really simple one to do first shot PTP. As with most stuff, usually more worried than I should be.

The Heyboer PT arrived this week, paid the invoice! Hell week at my job, so could not do any work. The chassis has the OT sitting on top, and most small holes drilled. Bitch of a thing to do with a hand drill, keeps moving off the punch mark. Only a few holes left to drill for PT and OT, then I can start wiring up. Determined on this amp to get every single hole drilled and double triple checked so I don't have to take the whole thing apart 3 times to drill a new hole .

I have a basic layout drawn, https://music-electronics-forum.com/...1&d=1565056792 this is about how I envision it would be built. Im not sure I did the ground chain right. and there is a connection not shown from the output tube cathode resistor to the negative side of the diodes. Working on it, will post an update. Thanks everyone for all the suggestions and help.

[tubeswell]

... most small holes drilled. Bitch of a thing to do with a hand drill, keeps moving off the punch mark. Only a few holes left to drill for PT and OT, ...

If you want accuracy sheet metal drilling with a hand drill, you need to make a small guide indent by hammer-punching a guide-indent for the drill bit. A 3 to 4 inch nail makes a handy punch. Lay the part of the sheet metal you want to punch hard against* a flat steel surface/bench (or metal vice) and hold the nail punch so it’s touching the metal right on the mark where you want to drill, and give the nail a single light and quick (but firm) tap with your hammer. This will make a tiny indent sufficient to guide the bit exactly where you want.

* this is important if you want to keep the sheet metal nice and flat ��