Tube Amp Archive

That 50k master is wrong, should be at least 500k. Just remove from circuit your 47k resistor.
About the hum, I bet it's reverb circuit ground.

I know this is an old post but I'm gonna ask anyway. What are you guys sticking the tweed down with before you lacquer? I used ordinary carpenter glue on mine recent build. The glue cured hard and kept the resonance of the uncovered pine. Another advantage, didn't smell. It gives you a lots of time...

Littlewyan, use your Ohm-meter to find windings first. You will have, most likely, one high Ohm reading, witch is primary, other one maybe 1/10 of it on the same side, witch is B+ choke and one or two connected together, very low reading - your secondary.(your 1,2 and4) Reading ac voltage without fi...

martin manning wrote:Wow! It's supposed to be 230 +/-10% as a standard, but in reality what that means is the UK can stay where it is at 240 and the EU can stay where it is at 220 with some margin.

A little bit of misunderstanding, Matec meant B+ 230V DC

[/quote]Really? That little cover fixed it even though the wires are exposed at nearly the same place?[/quote] Yes, it did stop the squealing. At the first I wanted to make small L shaped "fence", but I would have to remove the OT to drill a few mounting holes for it in the chassis, so I gave up and...

Here is an image of my SLO build. I had a problem with positive feedback at high volume settings until I covered the primary wires of OT.

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Well done identifying the bad grid leak resistor! But with a 1k cathode resistor, won't the cathode current and plate dissipation be rather different to Fender's design? I put a 1K, 25W resistor between the recto and the first reservoir cap. It drops the plate down to 347vdc, the cat to 28.1, givin...

I apologize, I deleted my post,tired eyes,
But this diagram could help :

http://dede92dubois.free.fr/maintenance ... igure1.JPG

Your mystery component is electrolytic cap 4microF/100V.
Cheers

There is nothing wrong with battery speaker test. Person just need to pay attention not to leave battery hooked up. :wink: Just a touch is enough to check the speaker, what bluesguitar probably did. Bluesguitar, did you try to check resistance of the speaker coil at tinsel wires ? I would assume (be...

Hi Silverfox, I'm glad you didn't get me wrong.Simply when you mentioned adding 3 or 4 preamp tubes later in your project, I had to warn you.
Without nice clean layout it would be impossible to have it running without hum or oscillation problems. Cheers, Damir

Hi SilverFox, you have to move input jack far away from output transformer wires. Best would be to the front panel. But, to be honest, I don't like your layout at all. I would suggest first to close these rectangular openings in chassis, find a nice scheme and verified layout and do a new build from...

About testing the OT in the amp, my main concern was ground connection to both primary and secondary. If we used small AC voltage at speaker output, high voltage on the primary of OT would find the path to the ground trough center tap, and B+ filter caps. Here is another method, it could work well, ...

Hi Littlewyan, I would say go for it ! I'm interested as well to try out other double triodes in output. I did try already 12ax7 and 12at7, I didn't like them. 12AU7 is really good.

Sure, what do you need ? Just ask. :D If you wanted to ask how to measure impedance, it's easy, but conjuctiv filter C9+R12 needs to be unsoldered at one end and center tap of primary ( going to B+) as well. Small AC voltage should be applied to secondary. Primary voltage should be measured at pins ...

Hi guys, just an update, after playing more with values of R9, actually I put resistor 5k6 in series with 100k pot, I have found I was wrong (again).
56K is way to go, what looked to my ears great at volume set at 10 with 5k6 is almost same as volume at 6 with 56k resistor.