Separate names with a comma.
Discussion in 'Amp Central Station' started by HD28, Sep 15, 2021.
V6 grid stopper carbon comp 1550 ohms
V6 screen grid ceramic brick made in Mexico 440 ohms
V5 grid stopper 1694 ohms
V5 screen grid 449 ohms
Should these be changed out?
Thanks again Wally!
I love reading your replies. Encyclopedic. Always a teachable moment.
Thanks, Jared….just sharing some tidbits I have picked up reading about and looking at amps.
HD28, like most things people debate the question of matching stoppers. I prefer them to be matched. Those two screen grid stoppers are not a bad match, but they are low numbers for 470ohm resistors. I order these in batches and go through the batch matching pairs…writing the value on the side of the ‘brick’. I don’t think Inhave ever seen anything below 460 ohms or above 480 ohms when looking at nominal 470s. .
Cool, nice amp, enjoy it!
Congrats! I have a lot of love for the Bandmaster.
I finally had some free time to install the parts on the band-master.
3 prong plug
Desoldered the death cap
Changed the grid stopper and screen grid resistors to matched pairs.
Changed all e-caps
Found a broken solder joint at the 100 ohm nfb resistor
Changed the 820 ohm nfb resistor because I thought it was toast. Because it read 98 ohms. The new one reads 94 ohms once installed. Lesson learned.
Wrapped the tremolo roach in some high tech lineman tape I had
Changed all 3 tremolo caps to .022 orange drops
Brought up to line power with variac
Adjusted the fixed bias to 69% on both 6l6’s. 450-455vdc 46-49mA
All caps read less than 0.002vdc on the ground side except V1 P6 0.13vdc
Voltage readings on all tubes are acceptable.
P6 412vdc, P8 0.114vdc, P1 460vdc, P3 0.002vdc
I swapped out the old Sylvania 12ax7 for a GT I had.
P6 396vdc, P8 0.04vdc, P1 445vdc, P3 0.0vdc
the trem is slow and strong
Very nice breakup at volume of 5
Where should I start troubleshooting V3?
I take it that you are speaking of the 1500ohm and 470ohm resistors on the power tubes?? If so, both of these applications are grid stoppers. One is the control grid stopper….the 1500ohm connected to pin 5 control grid. The other is the screen grid stopper connected to pin 4 screen grid. When speaking of the grids and applied ‘stoppers’ in beam tetrodes or pentodes, we need to maintain proper terminology, imho.
As for the tremolo circuit tube….V3. You say the circuit is functioning. Your cathode voltage readings show no voltage there. I don’t understand how the circuit functions without having proper bias voltage applied to that cathode?? Are you sure about those voltage reading?
One would wonder how it is working without the control grid being negative in relation to the cathode.
I don't either Wally. I will measure these again and report back...
Short the trem Jack and voila. Voltage galore!