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previous: Carl Z Bjorn;I'm not so su... -- 4/6/2000 11:48 PM

Re: More gain in a BF DR

4/7/2000 11:42 AM
Bjorn	Re: More gain in a BF DR Thank you John, Bruce and Carl. Your answers called for some more questions: John Stokes: You'd have to disconnect the 50k RA pot to get the boost. Thank you John, yes I did that (with an on/off pot.). – sorry, I forgot to mention this. Carl Z: The easiest thing is to sub out the 12AT7 driver tube and replace it with a 12AX7. Yes, I did that too – sorry. Must have an Alzheimer in the early stage… Carl Z: I'm not so sure using the DR power tranny is such a good idea… Actually I did install an extra transformer (2A, 6,3V) for the preamp filament supply (mounted on the filter cap pan – NO extra holes drilled!) because I thought the tranny was running hot – but the heat came from the power tubes so I removed it again and installed a small fan instead. Carl Z: ad farting: The cure for that is to replace the 220k grid leak resistors with 100k values. Also change the coupling caps from the driver tube to 0.047uF. That should tighten up the bottom end and should really get your Deluxe pumping! Would this mod tighten the bass further? Carl, you have to remember that you are talking to a total amateur… and I did decrease the cathode by pass caps (V2) to 1 and 10 uF. The 220k grid leak resistors – are those the resistors that connects with the Bias feed? The coupling caps from the driver – are those the 0.1 uF pair originally? Carl Z: While you're under the hood, you might want to consider changing the 470 ohm screen resistors to 1k 5 watts. This won't affect the tone but it's a reliablility upgrade The screen resisitors are 470 ohm at 5W. Why would I like to increase the value to 1K? What about slope resistors – what do they do? Is there any reason I would like to mess with them too? Bjorn

4/7/2000 11:42 AM

Bjorn

Re: More gain in a BF DR

Thank you John, Bruce and Carl. Your answers called for some more questions:

John Stokes: You'd have to disconnect the 50k RA pot to get the boost.
Thank you John, yes I did that (with an on/off pot.). – sorry, I forgot to mention this.

Carl Z: The easiest thing is to sub out the 12AT7 driver tube and replace it with a 12AX7.
Yes, I did that too – sorry. Must have an Alzheimer in the early stage…

Carl Z: I'm not so sure using the DR power tranny is such a good idea…
Actually I did install an extra transformer (2A, 6,3V) for the preamp filament supply (mounted on the filter cap pan – NO extra holes drilled!) because I thought the tranny was running hot – but the heat came from the power tubes so I removed it again and installed a small fan instead.

Carl Z: ad farting: The cure for that is to replace the 220k grid leak resistors with 100k values. Also change the coupling caps from the driver tube to 0.047uF. That should tighten up the bottom end and should really get your Deluxe pumping!
Would this mod tighten the bass further? Carl, you have to remember that you are talking to a total amateur… and I did decrease the cathode by pass caps (V2) to 1 and 10 uF.
The 220k grid leak resistors – are those the resistors that connects with the Bias feed?
The coupling caps from the driver – are those the 0.1 uF pair originally?

Carl Z: While you're under the hood, you might want to consider changing the 470 ohm screen resistors to 1k 5 watts. This won't affect the tone but it's a reliablility upgrade
The screen resisitors are 470 ohm at 5W. Why would I like to increase the value to 1K?

What about slope resistors – what do they do? Is there any reason I would like to mess with them too?

Bjorn

Replies:

Carl Z Bjorn;You said you ... -- 4/7/2000 11:07 PM