Looking for Supro Thunderbolt 6420 Build info

[tubeswell]

so the final question: 350-0-350v secondary power transformer from Classictone, which will result in higher B voltages, or a different brand that has about 300 -0 - 300v?

If you’re using SS diodes in a 2- phase rectifier, I vote for 300-0-300. Others may have different views.

[tubeswell]

Also, make sure you have enough currrent rating on the HT (and heater) winding(s).

For a ballpark guesstimate for a 300-0-300 HT, you want about 200mA to be sure the PT will cope well with the draw from a pair of 30W 6L6GCs under full signal. With a B+ = 424, figure about 390V plate-to-cathode with ~33V across the shared 200R bias resistor. Each plate idling at 77mA, plus around 6mA for each screen plus 3-4mA tops for the pre-amp tubes = 170mA. Under full signal, this could peak to a factor of about 1.2x*, - so that's close enough to 200mA.

* allowing for auto biasing and inefficiencies, and we want it to sag a bit with power chords.

And about 3A (minimum) for the heater winding (if you're just using 2 x 6L6 and 2 x 12AX7 and maybe a 6V lamp)

YMMV

Others may have different views.

[mikepukmel]

Also, make sure you have enough currrent rating on the HT (and heater) winding(s).

For a ballpark guesstimate for a 300-0-300 HT, you want about 200mA to be sure the PT will cope well with the draw from a pair of 30W 6L6GCs under full signal. With a B+ = 424, figure about 390V plate-to-cathode with ~33V across the shared 200R bias resistor. Each plate idling at 77mA, plus around 6mA for each screen plus 3-4mA tops for the pre-amp tubes = 170mA. Under full signal, this could peak to a factor of about 1.2x*, - so that's close enough to 200mA.

* allowing for auto biasing and inefficiencies, and we want it to sag a bit with power chords.

And about 3A (minimum) for the heater winding (if you're just using 2 x 6L6 and 2 x 12AX7 and maybe a 6V lamp)

YMMV

Others may have different views.

Thanks Tubeswell. Having a tough time finding that transformer. Found quite a few with higher B voltage secondary, but most with lower B have a lot lower current rating, unless maybe Im looking at the wrong spec. Hammond 290DX is 325vac quite a bit higher than 300. (Has a bias tap and 5v winding, that won't be used as well) 459v dc approx, vs 424vdc after rectifiers. Will send them an email, maybe they have a suggestion. The only transformer makers I know are Hammond, Classictone, both have spec sheets on their site, Heyboer, have to contact them, and Mercury, too pricey for most stuff.

[tubeswell]

THeyboer, have to contact them, ...

Heyboer also sells stuff via the WebetVST site. (They are pricier equivalents of the Weber spec transformers)

[mikepukmel]

Thanks Tubeswell, I 'll check them out.

[mikepukmel]

Layout question

I found a few layouts, this is one. critique is that some components are laid out so that a long wire has to go all the way across the board, to get to the tube pin. And the connection to pin8 on th PI was routed way to the far side of the board.





Tough for a weakly tech person to 'get there'. I keep comparing to classic Fender and Marshall layouts, where the wire from the tube to the board is really short, and components for a given tube are right near the tube on the board.

***
Working on a version of above.
What software do you guys used to draw out layouts? Something easy to use and cheap?

[Tony Bones]

Your drawings look like they might have originated here: https://el34world.com/Forum/index.php?topic=4089.0

The file named Supro Thunderbolt layout.sch was created using ExpressSCH which is part of the ExpressPCB package. It can be downloaded for free: https://www.expresspcb.com/expresssch/

ExpressSCH is meant for drawing schematics, but as shown, it can be used for layouts. Some of the super-nice looking layouts are made with Visio, but that's an expensive program.If you happen to alread own it, you can download a library of components from Steve Luckey's web site (scroll straight to the bottom or else you'll get stuck for weeks checking ot his builds): http://www.sluckeyamps.com/

If you want to take the time to learn, DIYLC is an awesome tool for creating layouts (totally free): http://diy-fever.com/software/diylc/

One thing that makes DIYLC nice (besides how nice the results look) is that you can use components that are actual size so you know everything will fit right. After installing DIYLC, you can download and install a library of actual size components from Doug Hoffman's site: https://el34world.com/Forum/index.php?board=26.0

When you're done, you can send the DIYLC file to Doug and he'll make a nice turret board for you for just a few bucks.

[mikepukmel]

Awesome, thanks Tony, will try them out when I get off work tonight.

[mikepukmel]

Well I got my by-hand drawing fairly close (I think, maybe). will try out the PCB software tonight.

Question for you all: I have a fiberglass eyelet board from one of the versions of Fender Deluxe AB763 that I tinkered with last year. I managed to get all of the first preamp tube components right across from the tube. Also managed to get the PI components fit where the channel 2 components went on the Fender.

There is so much room on the board, I fit the ss rectifiers, all of the electrolytic filter caps and dropping resistors at the other end of the board, where the tremolo and phase inverter went in the fender ckt. This leaves two potential problems:

1) The two grid (input) wires leading out of the phase inverter to the output tubes are pretty long to make it all the way over to the output tubes, pin 1 (parking pin for the grid stop).
2) The power supply caps, and dropping resistors are on the board right across from the output tubes.

All other wiring looks ok to my untrained eye. Leads are short (exc for grid wiring for output tubes).

So, questions:
- will longer output tube grid wiring cause a problem, is there something I can do to alleviate, maybe route them a certain way?
- Will having the HV power supply components on the board near the output tubes cause problems?
(e.g. oscillation, noise/hum).

Thanks!
As an aside, besides making the amp smaller (width wise), is there any good reason to have the power supply caps on the other side of the chassis, under a metal box, like Fender did?

[mikepukmel]

Its hand drawn, will get into PCB software asap. Don't laugh. OK go ahead, laugh, (I did too).

[loudthud]

Grid wires to output tubes look OK to me. When I do a layout for an existing board, I get a big sheet of paper and use the board to mark where all the eyelets are

[mikepukmel]

Grid wires to output tubes look OK to me. When I do a layout for an existing board, I get a big sheet of paper and use the board to mark where all the eyelets are

Thanks Loud! (Doesn't look so good, but that is what I did. Took a couple of pieces of printer paper, held over the board, and marked the eyelets out. Make copies of that, then drew components in by hand. Added about 11 new eyelets since this ckt components don't line up well with existing eyelets)

[mikepukmel]

Does the negative side of the power supply rectifiers need to be tied to the chassis, or can it just be hooked up to the - side of the filter caps and the power tube cathode?

[Helmholtz]

will longer output tube grid wiring cause a problem, is there something I can do to alleviate, maybe route them a certain way?

I would at least twist the grid wires. As the grid signals are opposite phase/polarity twisting will provide some shielding and produce a little capacitance (maybe 10 to 20pF) between the wires which may help to avoid oscillation.

[tubeswell]

Does the negative side of the power supply rectifiers need to be tied to the chassis, or can it just be hooked up to the - side of the filter caps and the power tube cathode?

Will hum less if it’s connected directly to the ground lead of the reservoir cap. I suggest following the grounding layout in Merlin Blencowe’s grounding article. (Especially Fig 15.12 and Fig 15.14) http://www.valvewizard.co.uk/Grounding.pdf