The Amp Garage

Thanks Martin-
Been reviewing Blencowe book and some other references, I believe I am grasping your explanation. Thank you for taking the time to help.
Byron W5FH

Thanks Martin- If you will bear with me, I still am confused in regards to preamp circuit V1a. The gain stage is supplying the DC voltage to the 1.8M and 1 M voltage divider pair from plate side of the 100K plate load resistor. Won't this DC voltage be varying up/down at an audio rate as this gain s...

If someone with more understanding can explain to me please- I have attached two Hiwatt preamp schematics to refer to. What I cannot get my head wrapped around is how the bias "regulator" triode can output the same bias voltage to phase inverter grids (in vicinity of 73 vdc) when it has its grid vol...

Thanks for comments Mark and thank you for the great Hiwatt site and all of the info, much appreciated.
Byron W5FH

Hey there cdemike- To answer your question about my builds using the Hiwatt fixed bias P/I I used the separate triode (V3-B) of 12AX7 (no audio passing through it) to supply grid bias to phase inverter. The circuit I used (for fixed bias and P/I only) is identical to the one shown on the Hiwatt earl...

Thank you cdemike! I have studied that two-input Jimmy Page Hiwatt preamp and your excellent write-up. It bothered me looking at the 100K resistor coming off of B+ line that feeds the plate circuits of both triodes of V3. The first section of V3 is the post master volume gain stage and has its own 1...

Hello- I am researching the HiWatt fixed bias phase inverter. Have done much searching, read the Amp Books discussion and studied Mark Huss site. I see there were two versions - the early version where the signal was passed to P/I through a coupling cap into the DC bias/cathode follower triode and t...

Built on Super Reverb blank steel chassis. Pair of KT-88's into an O'Netics A-431 level #1 output (not using UL taps). Modified Astroverb preamp, HiWatt fixed bias phase inverter/presence circuit, Sluckey Tremonator vibrato and Jensen line-out circuit per application bulletin. The little JT-11 trans...

Hello- For readers who have a few moments I am seeking advice on speaker recommendations for an amp I just finished. It is a copy of the Astroverb preamp feeding into a fixed bias Hiwatt phase inverter driving a pair of 5881's. P/I and power section designed to be as clean as possible. Using a sligh...

I believe you are discussing the standby circuit published by Mr. Blencowe. I have used this in several builds. I have remained with the 47K series resistor. My voltage at preamp nodes is around 130 VDC to 180 VDC from checks in the several builds. Residual sound from amp has not been an issue yet. ...

Hello- I apologize if this is a little off-topic but I cannot get the info I need from phone calls or searches. A friend brought over one of the Martin B-20WN custom made guitars. This is a special edition made in the late 1990's with a pickup that was supposed to be sonicly equivalent to the origin...

Thank you all for the nice replies and info- I have been researching UL more and have found a number of guitar amp designs using it. Some are using grid stoppers. Of interest to me was some discussion of OT screen tap "percentages" of which the 40% region appears most often used. Some users of UL sa...

I have some questions regarding output transformers: I have been studying the Edcor push-pull audio output transformers with some interest due to their screen taps at 40%. I recently did a build using the Amp Supply 8025-H output transformer using a pair of 5881's which worked out very well. I was c...