Champ 5F1 with vibrato

[dinkotom]

End bells are usually just for looks. Does the PT have a shield?

'fraid not...does it take a lot of work to shield it? I could try and put some copper strip around it but I'd really need a detailed guide. Any links on how to do this?

In regards to the sovtek 5Y3, you can always put one or more 5W 9V-15V reverse-biased (anode/banded ends pointing to ground) zener diodes in series with the centre tap-to-ground off the High Tension winding, in order to bring down the B+ if you think that rectifier doesn't drop enough voltage. But I'd wait until you fire it up and see how much B+ you get first.

Good to know about this, but I have an old GE JAN 5Y3WGTA (from the first Champ I built 10 years ago), so I'll use it instead.

[dinkotom]

I'd also use a 1 amp slo-blo or a 1 amp MDL fuse.

...doh! Just found out I don't have any 1A slo-blo's around, just 2 and 3A, and of course local electric supply shops don't carry them. Will I be pushing my luck with a fast blo?

[tubeswell]

'fraid not...does it take a lot of work to shield it? I could try and put some copper strip around it but I'd really need a detailed guide. Any links on how to do this?

Its just a grounded band of copper foil around the iron and windings all in one. Cut a strip of copper foil wide enough to cover the windings and wrap it neatly around the iron/and windings and solder the two ends of the copper foil together. Use a couple of aluminium or steel metal strips with a hole at each end on each side (i.e. 4 strips altogether - one each side of the winding bolted through where the iron interleaving assembly bolts are) to keep the copper close to the windings.

[tubeswell]

2A slo blo will be better than 2A fastblo

[dinkotom]

I guess I can almost figure out to do this, I'll try.

2A slo blo will be better than 2A fastblo

scuse I wasn't clear, I do have a 1A fastblo. So, what's safer, 1A fast blo or 2A slo blo?

[tubeswell]

I guess I can almost figure out to do this, I'll try.

scuse I wasn't clear, I do have a 1A fastblo. So, what's safer, 1A fast blo or 2A slo blo?

Its more a matter of what will work. A fastblo won't take the peaks and troughs as well as a slo-blo. You may find it blows fuses more.

[dinkotom]

Well, shield or no shield, we couldn't wait and powered it up and got no sound at all! After measuring voltages again and staring at it for about half an hour,I noticed I didn't connect .022 cap going from first the plate to vol pot!
Fixed it and it works! And it hums a little, but who cares... the sound is as expected, raw and gnarly (speaker is Celestion G10S), but it's farty when overdriven (I already lowered the first cathode cap to .22), tremolo works fine, and this thing is LOUD, much louder then my stock 5F1. I could perhaps tweak it a little to get a clearer bass freqs, but the owner loves it as it is.
Please check the voltages on Sovtek 6V6:
plate: 356VDC
screen: 295VDC (seems a bit low?)
cathode: 17VDC

One thing left to do is a vibrato cable, would a regular guitar cable be OK?

[tubeswell]

Those voltages are about right.

Guitar cable is fine. The shield is the return wire

For the fartiness you could try lowering the value of the first coupling cap from 22nF(.022uF) to 10nF(.01uF), but personally I like the sound of the 22nF there. Another thing you can do is up the reservoir filter to 40uF - by 2 x 20uF in parallel in the first position (but I wouldn't go any higher than that, or you'll do the rectifier in). The hum is normal in those things, unless you use a CLC filter (and the best place for that is between the rectifier and the plate node filter cap)

[dinkotom]

Thanks, I'll try these cap values and see, I know my nephew won't mind.
And big thanks to everyone who helped with their suggestions and ideas, making this such a fun project.
I did learn quite a bit building this amp and as I am already in preparation for the next build, (Magnatone 213), expect a new batch of dumb questions soon...

[andrew_k]

Don't know if you're still around to read this, but I'm at the end of building a very similar champ (6G2 preamp into BF vibrochamp) and have a tip for you to get rid of the excessive "farting" when it's turned up -- entirely remove the cathode bypass cap off the second triode; probably a 10uF.
The BF tonestack eats a lot more gain than the one-knob stack we're both using, and as such doesn't need as much gain in the next stage to make up for it. 10uf was terrible, 5uf better, 1uf was usable if you want more breakup, but no cathode bypass cap was my preferred option.
I have a 6G2 clone and a '78 vibrochamp that I was comparing to and with no bypass cap on the second triode it's exactly the middle ground I was after.