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previous: Bjorn Thank you John, Bruce and Carl. You... -- 4/7/2000 11:42 AM

Re: More gain in a BF DR

4/7/2000 11:07 PM
Carl Z	Re: More gain in a BF DR Bjorn; You said you subbed in a 12AX7 already. I take it you're still looking for a little more drive. What did or didn't you like about that change? Re: grid leak resistors and coupling caps. Yes these are the ones that are originally 0.1uf They are the last set of caps nearest the power transformer on the main board. They hook up to the two V shaped pairs of resistors. The 220k pair hooks up to the bias pot. These are the two you want to change to 100k. Using the normal values of 100k/0.1uf will give you a -3dB point of about 7 Hz. Knocking back these values to the ones I suggested will increase this value to around 31 Hz. Somebody check my math here...I'm going by memory, which seems to be getting fuzzier by the day. The increase in the size of the feedback resistor will add a lot of mush to the tone of the amp in it's own right. So, changing these parts should really tighten it up. I really doubt that the 470 ohm resistor is 5 watts, 1 watt carbon comps are pretty big. All this change is going to do is lower the screen current a little and increase the screen to plate voltage difference. The tubes will be a little happier with this arrangement. Regarding the slope resistor, changing this value will change the midrange response of the amp. All other things being equal, if you increase the value from say 100k to 150k you'll scoop some of the mids out. Conversely, changing the 100k to 56k will increase your low/low mid response. The tone stack is a good place to play with values when voicing your amp. Change only one value at a time. Leave them in for a few days to get accustomed to the changes and let the newness wear off. Little changes here can make a big difference in the way your amp reacts! Regards; Carl Z Summit Amps

4/7/2000 11:07 PM

Carl Z

Re: More gain in a BF DR

Bjorn;

You said you subbed in a 12AX7 already. I take it you're still looking for a little more drive. What did or didn't you like about that change?

Re: grid leak resistors and coupling caps. Yes these are the ones that are originally 0.1uf They are the last set of caps nearest the power transformer on the main board. They hook up to the two V shaped pairs of resistors. The 220k pair hooks up to the bias pot. These are the two you want to change to 100k.

Using the normal values of 100k/0.1uf will give you a -3dB point of about 7 Hz. Knocking back these values to the ones I suggested will increase this value to around 31 Hz. Somebody check my math here...I'm going by memory, which seems to be getting fuzzier by the day.

The increase in the size of the feedback resistor will add a lot of mush to the tone of the amp in it's own right. So, changing these parts should really tighten it up.

I really doubt that the 470 ohm resistor is 5 watts, 1 watt carbon comps are pretty big. All this change is going to do is lower the screen current a little and increase the screen to plate voltage difference. The tubes will be a little happier with this arrangement.

Regarding the slope resistor, changing this value will change the midrange response of the amp. All other things being equal, if you increase the value from say 100k to 150k you'll scoop some of the mids out. Conversely, changing the 100k to 56k will increase your low/low mid response.

The tone stack is a good place to play with values when voicing your amp. Change only one value at a time. Leave them in for a few days to get accustomed to the changes and let the newness wear off. Little changes here can make a big difference in the way your amp reacts!

Regards;
Carl Z
Summit Amps

Replies:

Bjorn Thanks Carl, I will try the changes... -- 4/7/2000 11:58 PM
Bjorn Carl, I was a bit fast responding t... -- 4/8/2000 12:06 AM
Bjorn Feedback Carl Z -- 4/12/2000 8:15 PM