martin manning wrote:Check the high voltage and filament wiring carefully for potential shorts, i.e. leads close to chassis-grounded screws, etc. Maybe playing it louder is shaking out more solder blobs.
martin manning wrote:Check the high voltage and filament wiring carefully for potential shorts, i.e. leads close to chassis-grounded screws, etc. Maybe playing it louder is shaking out more solder blobs.
I gave it another look and I don't see anything that would be causing an issue with B+.
Soldering seems to have been your Achilles Heel on this one. I think you said you went up to a 25W iron for this job? I don't know what you have, but a temperature-controlled soldering station is well worth the cost. People will have their personal preferences, but I like my 50W Weller WESD-51. A tool like this works very well for everything from large solder lugs on jacks and switches to tiny PCBs and 32AWG wire.
martin manning wrote:Soldering seems to have been your Achilles Heel on this one. I think you said you went up to a 25W iron for this job? I don't know what you have, but a temperature-controlled soldering station is well worth the cost. People will have their personal preferences, but I like my 50W Weller WESD-51. A tool like this works very well for everything from large solder lugs on jacks and switches to tiny PCBs and 32AWG wire.
I looked at a station but I knew I would want a good one if I were to make the investment. I'll look at the Weller you have and give it some thought. On this project I used a 15W, 25W and a 150/230 gun for the bus grounds. A single station would streamline things nicely.
I have the 3 amp fuse installed and so far so good. I thought I saw the jewel dim a time or two when I pushed the vol to full. I'm gonna stop and dial in the bias before I play anymore.
I know truly matched tubes are hard to come by and I know the DC resistance of the 2 OT legs is not going to be the same so I averaged them. 50R+44R = 94/2 = 47R
With my bias voltage set at -50 I had 22mA. I dropped it to -40 and got to 27mA and only .630v on the hottest OT leg.
My question is, what's the stopgap here? Do I care how close the bias voltage gets to zero as long as I get the idle current in line? Is -30 or -25 healthy voltage so long as the proper dissipation is attained?
Guitarnut wrote:On the subject of biasing the power tubes.
I know truly matched tubes are hard to come by and I know the DC resistance of the 2 OT legs is not going to be the same so I averaged them. 50R+44R = 94/2 = 47R
With my bias voltage set at -50 I had 22mA. I dropped it to -40 and got to 27mA and only .630v on the hottest OT leg.
My question is, what's the stopgap here? Do I care how close the bias voltage gets to zero as long as I get the idle current in line? Is -30 or -25 healthy voltage so long as the proper dissipation is attained?
Peace,
Mark
Like the Brown series, the Tweed Bassman sweet range is only 30-34ish, leave the 38-40 for the Silverface stuff. If I could get the cathodes to around 32,I would call it a day.
ToneMerc wrote:
Like the Brown series, the Tweed Bassman sweet range is only 30-34ish, leave the 38-40 for the Silverface stuff. If I could get the cathodes to around 32,I would call it a day.
TM
Thanks TM and thanks for your input along the way!
That's about where I landed. I'm at 30mA right now and I'm loving it. I have a Thinline Tele that I built a few years back with Texas Specials and it absolutely oozes sweetness with the normal vol dimed.
As much as I have struggled with this build, the results are well worth it. Just can't imagine that a box of parts could turn into so much happiness!
I need to get the chassis installed and get into the studio before the sun goes down and the neighbors start complaining.
Set the bias level where it sounds best for sure, but you should adjust the bias circuit to get the available range positioned to cover different sets of tubes. You don't know how the set you have in there compares to the average, but you should tweak it so that the bias pot is more or less centered. You'll want to put those 1 ohm resistors on the cathodes to make the measurement easier too.
