Can I use a different hookup for the bias circuitry.

[Mike_J]

Fired up the amp with the lamp limiter and rectifier tube in only. It started out with little light and went to no visible light. Figured that meant I was okay to go. Disconnected the lamp limiter and measured the range of voltage the 10K has and it went from -32VDC to -66VDC. Figure I am okay to proceed to the next step. Now I need to figure out what the next step is. Unfortunately I know what the next step is. Doing it over and leaving the bias pot at the highest negative voltage level. Got so excited I forgot to do that important step.


Thanks
Mike

[pdf64]

Leave the LBL in play until reliable operation, eg valves working with signal, has been proven.
When that’s done, take it out of circuit, take true voltages and set bias etc.

[Mike_J]

Leave the LBL in play until reliable operation, eg valves working with signal, has been proven.
When that’s done, take it out of circuit, take true voltages and set bias etc.

Will do. Thanks.

[Mike_J]

Leave the LBL in play until reliable operation, eg valves working with signal, has been proven.
When that’s done, take it out of circuit, take true voltages and set bias etc.

Wherever you said 23 watts of dissipation was the center not the maximum is consistent with what Rob Robinette is using for his 5881 biasing. He is using 26 watts as the maximum so I created a chart with the 26 watts and will consider the 70% dissipation at 26 watts as my max for biasing purposes.


Thanks
Mike

[Mike_J]

Looking at my book and came up with this Humble schematic from 1997 which I have attached. In all of his ecap stages Humble had two caps in series with 470K resistors across all of them. There is also a close up clandestine microchip type markings on the schematic which I circled and took a closeup picture of which I suppose identified values someone was trying to hide. The extent people will go to try to uncover things other people are trying to hide is staggering. Thought it was a little bit of interesting history.


I read something by Merlin, Willabe suggested, http://www.valvewizard.co.uk/smoothing.html commenting on smoothing and filtering the power supply. Specifically dealing with resistors placed across ecaps in series to make sure power is being shared somewhat equally by both caps.  “The resistors should be equal to 50/C or less, so two 100uF capacitors would each need a 500,000ohm resistor (470k would be the obvious choice). These also act as bleeders when the amp is switched off.”
I guess he is talking about farads which is why he is multiplying by one million? Also, he says or less. By less, does that mean the Fender value of 220K is fine? Also, if my calculations are correct, I would need a pair of one meg resistors across a pair of 47uF in series. Does this make any sense to anyone?
Another thing Merlin recommends is;
“If space is tight then we might want to use smaller caps for the preamp, say 22uF. For decent hum reduction we should push the cut-off frequency down to a really low frequency, like 1Hz. This will mean the dropping resistors need to be at least:
 R = 1 / (2 pi f C) = 1 / (2 pi × 1 × 22×10^-6 ) = 7,234 ohms.
 However, since 6mA of preamp current will have to flow in the first resistor, this would drop quite a lot of voltage, maybe too much. We might therefore want to relax the first resistor to 4.7k, say, which would drop only 6mA × 4.7k = 28V and dissipate 0.006^2 × 4,700 = 0.17 watts. Later dropping resistors could perhaps be larger, although 22uF and 4.7k give a cut-off frequency of 1.5Hz which is quite respectable.”
 This would mean a 22uF cap for V2 and a 22uF cap for V1 with 4.K dropping resistors to each ecap whereas they currently share one 22uF for both tubes. When both tubes share a 22uF cap there is a 10K dropping resistor. Anyone see an advantage of increasing the voltage to the V2 plate load cap? By the time you get to V1 the plate voltages would be nearly the same. Have 44uF on V1 and V2 now combined as per the Bassman reissue schematic.


Thanks
Mike

EDIT: parse URL