Dukane 1A385

[sluckey]

When you "dime" that tone control it is basically removed from the circuit and you are experiencing all the treble the amp has to offer. But you can make the amp seem to have more treble by reducing the bass. Do this by replacing those 25µF cathode bypass caps on the preamp tubes (not the power tubes) with 5µF, or 1µF, or even .68µF. Easy to do and may just get you the brightness you seek.

[angelodp]

Ok yes of course. 10uf seems to make my ears happy (having lost some upper freqs like most my age), and the tone knob is more dynamic now, all in all, I like it. Man this is also a loud amp, so the MV is quite useful.

Best A

[angelodp]

Switched out the V2 Cathode cap from 25uf down to 10uf and that was a good move as well. This cleaned up the 'stang' on the treble notes and I am very much enjoying this amp. It is touch sensitive and cleans up nice as I roll the guitar vol down. I am running it kinda wet/dry, with the reverb just on one channel, I know its all mixing downstream. Waiting for an RSA 5Y3 to replace the JJ. I did go back to the 12AU7 for the concertina. I guess the iron in this amp is pretty good stuff. Can I date the amp through the PT 710 4097. 549942. and OT TTI3866. 7102054

[angelodp]

Hi, I do not understand what is happening completely around V2. The signal comes into the lower grid, it is biased by the cathode RC, the signal goes up to the plate then onto the cathode of the upper triode. I do not understand that .1uf and 1M arrangement. If someone would kindly take me through what is happening with this tube.

[martin manning]

It's a cascode. See http://www.valvewizard.co.uk/cascode.html

[angelodp]

Ah, so hi-gain low noise. That explains this amp a bit more. Its is remarkably quite and does have a fair amount of gain. Now Fred's Tweedle is a fire breather, this is not. N ow have the RCA 5Y3 in and will swap in an Ampirex Bugle Boy at V1. I will post my voltage chart in a bit. Have to read up on Aikens article as well on Cascode.

[angelodp]

I have tried number of one knob variations for tone with no success. Given the current schematic I could use any suggestions on making this tone knob more useful, as in rolling from more bass to more treble. Is that 470k way too much?

Here is tone stack from the net, Inserted this and I hear a very very low signal? Where am I going wrong.

[angelodp]

Pulled all that out and got out the decade boxes. Made some adjustments to the two volume pots and tone pot as is and have a good solution.