1960's Supro Thunderbolt scratch build copy

[lovelash]

I'm about to finish up construction and will be applying power to it sometime this weekend. Attached are the schematic I started with in PDF format and the other is the schematic that was actually built after adding a stand by switch, grid resistors, and a couple other details or two that were suggested by forumites.

Is there anything that looks like a mistake/oversight ?

All I have left to do is wire the heaters, grounds, and a few other connections. Whattaya think?

Thank you man for taking your time out and posting a helpful information.

Really appreciated your efforts. Have a good day!

Regards

[PrummelJR]

A proper cathode resistor to get your amp in the same range can be calculated or you can sub in different types and figure out what the dissipation is, and see if you like the tone or not. The comment on the schematic regarding using a 240 ohm if desired was for people who didn't want their tubes to wear out so quickly

[HaroldBrooks]

Ok I tried a 240 ohm 5W resistor just for a test. Here's what voltages I got.

V4 - 71mv across 1 ohm resistor
p3- 442v
p4- 435v
p5- .111
p8- 35.93


V3 - 68mV across 1 ohm resistor
p3- 442v
p4- 435v
p5- .163
p8- 35.95

I kinda like the tone better with the 270 ohm resistor in, so I'm going to switch back. But I have a question about wattage calculation. Chuck you had mentioned "Measure the cathode voltage and divide by the cathode resistance. This is your current. Multiply that number by your "plate to cathode" voltage to get your "watts at idle" figure"

How do I figure the cathode resistance? I entered in 240 ohms and came up with around 60w per tube. If I use the voltage across the 1 ohm resistor method for calculating current, then I get around 28W per tube. Where was my error?

I have several valco amps using 6973 tubes (not 6L6s), and using a slightly bigger Cathode resistor didn't change tone all much, but put the ouput tubes in a safer region. I think in the amp world there are some who perpetuate a misguided fixation on running the plate idle dissipation as high as possible, in the false belief that an amp will sound "Hotter" and more aggressive and maximize power. But as with many things, there are several ingredients in the amp "Stew" that are responsible for a good sound and high output.

Last on my personal list would be running the output tube plate dissipation on the verge of red plating, particularly if it didn't do that back in the 1960's with the lower wall voltages. Remember the wall voltages have increased since that amp was designed, so you may be required (by vintage tube amp law ? ) to adjust your amp, to set things back to right so it runs like it did back in the day.

Only recently I realized how important Screen voltage is to power output, more so than the last few watts of plate dissipation. You saw that first hand when you dropped the size of the too large screen resistors and the amp woke up, so that's a bit more important.

I vote for sticking with the 270ohm or perhaps the 300ohm cathode resistor, as the tone difference should be minimal, and the amp and tubes will run cooler and longer, IMHO.

[mort]

Haven't been amping in a while so haven't logged in. Had recent notifications on this thread so looked back through it. Sadly, the guy that this was built for, Paul Slagle of Pittman Guitars, died 2 days ago. I built 2 more amps for him after this one and I have 4 of his beautiful guitars. Here's the most recent one he did for me. I'll miss that guy more than most people I've known in my life even though we never actually met in person. He was a real gem. So long old buddy.

[Leo_Gnardo]

Here's the most recent one he did for me.

That is one beauty of a Telecaster! Is there some kind of polka dot pattern on the control panel, or am I seeing a reflection of some sort of acoustic tile?

I like the little flat spot where the output jack is mounted. Nice practical touch.

[mort]

That is one beauty of a Telecaster! Is there some kind of polka dot pattern on the control panel, or am I seeing a reflection of some sort of acoustic tile?

I like the little flat spot where the output jack is mounted. Nice practical touch.

That's just reflection of the pegboard where he hangs his tools and such. You can see it on the body too.


And as for the amp.. here's a video demo his friend did for me. I've been on memory lane ever since I got the news about his death.

[Pedro Vecino]

Do you remember what cabinet it is and what speakers it used?
Thanks!

[mort]

Do you remember what cabinet it is and what speakers it used?
Thanks!

In the video I have no idea. On the original it was a combo I believe but I don't know what speaker it was.

[g1]

By the way, good to see you back around, former 'semi-noob'.

[mort]

By the way, good to see you back around, former 'semi-noob'.

Thanks!

I kinda move around between amp building, kayak fishing and football card collecting as my hobbies. The season of amp building again feels like it's coming back around.

[Chuck H]

Thanks!

I kinda move around between amp building, kayak fishing and football card collecting as my hobbies.

Kayak fishing is very popular here in the PNW as well. Though the species are probably very different and a neoprene wet suit is a must here. I like to fish but I haven't gotten up the nerve to try kayak fishing in these hypothermic waters yet

[Enzo]

How many kayaks can you catch on an average day?

[Chuck H]

How many kayaks can you catch on an average day?

I told a friend from Cali that I took up mushroom hunting here in the PNW. He asked me if I use a knife or a gun.?.

[xpaceseven]

Have you ever used the Tone Stack Calculator? That tone stack is on there as the Big Muff one. You can see how different values affect the frequencies being cut.