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More gain in a BF DR

4/6/2000 7:57 PM
Bjorn	More gain in a BF DR Hello to ya all Ampagers! I’m the (happy) owner of a BF DR. The DR is modified (yes, its not a museum piece…) and carries 2 Svetlana 6L6 biased to 36 mA (the PT seems to be able to handle this change OK). The filter section is changed to SR specs. This was done in order to increase voltage and headroom in the preamp section (I’m hope I’m right about this . In order to reduce flatulence the CBC in the first gain stage (V2) was changed from 22 uF to 1 uF and in the second gain stage to 10 uF, with a very nice result. Then the coupling cap by the PI was changed from 0.001 uF to 0.01 uF. To get some more gain the NF resistor was changed from 820R to 47K (I think) and V1 was pulled out. The tone stack was changed to 0.022 and 0.047 uF. The speaker (Oxford) really sucked and I had two old CTS 10´ speakers from the SR that I wanted to try. I made a new baffle and installed the CTS pair. I was unable to wire the speakers to get the 8 ohms required and settled for 4 ohms instead. This mismatch really made a BIG tonal difference – it did “open up” the amp and I believe increased wattage as well. When reading posts here on Ampage there has been some threads mentioning changing the value of the slope resistor and the cathode resistor (V1), and other resistors as well, in order to increase gain. I love the sound of this amp but I would like to get just a little bit more gain (maybe also some more presence). Any suggestions? Bjorn

4/6/2000 7:57 PM

Bjorn

More gain in a BF DR

Hello to ya all Ampagers!
I’m the (happy) owner of a BF DR. The DR is modified (yes, its not a museum piece…) and carries 2 Svetlana 6L6 biased to 36 mA (the PT seems to be able to handle this change OK). The filter section is changed to SR specs. This was done in order to increase voltage and headroom in the preamp section (I’m hope I’m right about this ;-)

. In order to reduce flatulence the CBC in the first gain stage (V2) was changed from 22 uF to 1 uF and in the second gain stage to 10 uF, with a very nice result. Then the coupling cap by the PI was changed from 0.001 uF to 0.01 uF. To get some more gain the NF resistor was changed from 820R to 47K (I think) and V1 was pulled out. The tone stack was changed to 0.022 and 0.047 uF. The speaker (Oxford) really sucked and I had two old CTS 10´ speakers from the SR that I wanted to try. I made a new baffle and installed the CTS pair. I was unable to wire the speakers to get the 8 ohms required and settled for 4 ohms instead. This mismatch really made a BIG tonal difference – it did “open up” the amp and I believe increased wattage as well.
When reading posts here on Ampage there has been some threads mentioning changing the value of the slope resistor and the cathode resistor (V1), and other resistors as well, in order to increase gain. I love the sound of this amp but I would like to get just a little bit more gain (maybe also some more presence). Any suggestions?

Bjorn

Replies:

bill pull the tremelo tube for more gain... -- 4/6/2000 9:43 PM
Carl Z Bjorn;I'm not so su... -- 4/6/2000 11:48 PM
Ricky more efficient speakers -- 4/11/2000 7:04 PM