More tubes on the way from Antique Electronic Supply in Arizona. Very nice people to deal with.
Not sure what's going on with heaters. Received Variac yesterday. 110 vac supply to amp gave 6.3 vac heater supply. 5.3 amps. Turned on today and heaters at 6.0 vac with 110 vac into amp . Took 115 vac into amp to get 6.3 vac heater supply. 125 vac wall voltage gives 6.8 vac @ 5.5 amps.
At 6.3 vac the 12AX7/7025 tubes pulled .3 to .4 amps each. 4x6L6 tubes pulled 4.2 amps. Pulled two and remaining two pulled 2.1 amps. Replacing entire quad because AES did not have single tube to match my set so did not test any further.
More tubes on the way from Antique Electronic Supply in Arizona. Very nice people to deal with.
Not sure what's going on with heaters. Received Variac yesterday. 110 vac supply to amp gave 6.3 vac heater supply. 5.3 amps. Turned on today and heaters at 6.0 vac with 110 vac into amp . Took 115 vac into amp to get 6.3 vac heater supply. 125 vac wall voltage gives 6.8 vac @ 5.5 amps.
At 6.3 vac the 12AX7/7025 tubes pulled .3 to .4 amps each. 4x6L6 tubes pulled 4.2 amps. Pulled two and remaining two pulled 2.1 amps. Replacing entire quad because AES did not have single tube to match my set so did not test any further.
You probably know this already but take a look at the getters in the tubes; if they have turned milky white it could indicate the vacuum has been breached. If so, that could explain the extra current draw. Modern tubes also, have a reputation for pulling more current than the datasheet specs and the getters in modern tubes are not always perfectly dark but rather, mottled. The tubes, individually, should be okay if the glass is clear and hasn't had a condensate (the milky white) form on its surface. The extra current, as a relatively low percentage as here, is not necessarily a bad thing, a bit like a turbo on an engine, but if the heaters are burning yellow, you are looking at a shorter lifespan and I am thinking you don't have this problem when the voltage is down around 6.3V. If you suspect a tube has turned gassy, and is pulling a lot of current (insert your own idea of "a lot" here) along with flashing and arcing, it should be discarded to prevent any damage to your transformers. Your problem doesn't seem to be the current they are pulling so much as the mismatch. You do best to stay your horses and wait for the new matched quad before doing any further testing, you might get on with testing though if you remove a pair of tubes (including the one with the mismatch) and test in 50W mode.
Regarding your different readings from one day to the next, did you leave the amp to thoroughly warm-up before each test? Burning the amp in for up to 40 hours is also a good idea. Everything should stabilise over time.
More tubes on the way from Antique Electronic Supply in Arizona. Very nice people to deal with.
Not sure what's going on with heaters. Received Variac yesterday. 110 vac supply to amp gave 6.3 vac heater supply. 5.3 amps. Turned on today and heaters at 6.0 vac with 110 vac into amp . Took 115 vac into amp to get 6.3 vac heater supply. 125 vac wall voltage gives 6.8 vac @ 5.5 amps.
At 6.3 vac the 12AX7/7025 tubes pulled .3 to .4 amps each. 4x6L6 tubes pulled 4.2 amps. Pulled two and remaining two pulled 2.1 amps. Replacing entire quad because AES did not have single tube to match my set so did not test any further.
You probably know this already but take a look at the getters in the tubes; if they have turned milky white it could indicate the vacuum has been breached. If so, that could explain the extra current draw. Modern tubes also, have a reputation for pulling more current than the datasheet specs and the getters in modern tubes are not always perfectly dark but rather, mottled. The tubes, individually, should be okay if the glass is clear and hasn't had a condensate (the milky white) form on its surface. The extra current, as a relatively low percentage as here, is not necessarily a bad thing, a bit like a turbo on an engine, but if the heaters are burning yellow, you are looking at a shorter lifespan and I am thinking you don't have this problem when the voltage is down around 6.3V. If you suspect a tube has turned gassy, and is pulling a lot of current (insert your own idea of "a lot" here) along with flashing and arcing, it should be discarded to prevent any damage to your transformers. Your problem doesn't seem to be the current they are pulling so much as the mismatch. You do best to stay your horses and wait for the new matched quad before doing any further testing, you might get on with testing though if you remove a pair of tubes (including the one with the mismatch) and test in 50W mode.
Regarding your different readings from one day to the next, did you leave the amp to thoroughly warm-up before each test? Burning the amp in for up to 40 hours is also a good idea. Everything should stabilise over time.
The horses are stayed
As soon as I got off the phone setting up the return I pulled the tubes and put them back in their original boxes and amp has not been powered up. Close inspection of tube shows no signs of vacuum loss or gas intrusion, it looks identical to the others.
Anxiously waiting for the replacements which are supposed to be delivered today. I agree a good burn-in is a good idea, I just did not want to do so with the elevated heater voltage. Now I can do a burn-in with the Variac if I need and address the heater voltage later if that issue returns.
Now you have the variac, something else you might want to consider and which may go part way towards stabilising the circuit, is to form your caps. Basically, fresh modern electrolytics don't really need this but it's likely you will have some that were sitting on a shelf longer than others before you built them into the circuit. Forming them doesn't do any harm and though I believe Ken Fisher used to do this over 24 hours, I think you can get the same results in a fraction of the time - especially with recently made caps. At worst, it will probably give your caps a bit more longevity.
Received the power tubes, another set of Sovtek 6L6WXT+ that are "Apex Matched". This set is looking good so far. Started at 110 volts with Variac, heater voltage was 6.0. Increased input voltage until 6.3 vac achieved on heaters, input voltage at 116 vac. Heaters pulling 5.2 amps at 6.3 vac.
Let tubes warm up a good 5 minutes or so then out of standby. Set bias to 20mA @ 225 volts, pretty cold. ALL 4 tubes pulling 20mA, nicely balanced. Both bias voltages reading -47.1.
CL1, CL2 and OD1 plates at 180v, OD2 at 183. PI at 275-277.
Gonna let it run like this for at least an hour or so. No signal, nothing plugged in except 8 ohm dummy load. Haven't hooked up a speaker yet to check noise level. Need to keep house quiet, long story involving 9 three day old French Bulldog puppies and a wife that hasn't had much sleep in same 3 days....
Got our 2x12 and plugged it in. VERY quiet now, hiss is gone! Now it reacts as I expected it to, a bit of hiss and slight hum variable with volume controls and swithces. Right now the heater circuit is disconnected and my meter is completing it so some 60 cycle hum is expected. This is all with nothing plugged into the input or effects loop. Gonna let it burn in more and when I get a chance plug in a guitar.
GAStan wrote: ↑Sat Sep 30, 2023 7:12 pm
Got our 2x12 and plugged it in. VERY quiet now, hiss is gone! Now it reacts as I expected it to, a bit of hiss and slight hum variable with volume controls and swithces. Right now the heater circuit is disconnected and my meter is completing it so some 60 cycle hum is expected. This is all with nothing plugged into the input or effects loop. Gonna let it burn in more and when I get a chance plug in a guitar.
Sounds like progress. Something you might try now, if you want to keep the noise down, is to hook up a radio station on the input and run the amp on the dummy load.
Figured out what was going on with the heater voltage. I was connected directly to the heaters measuring heater voltage. When I removed the meter and reconnected the heater wiring the voltage went to 7.3 vac. I had not accounted for the resistance of the meter. I put it back in the circuit and it was dropping .6vac.
Now I have the numbers I need to calculate resistance required:
125vac wall
0.6vac meter/resistor
7.3vac transformer
6.7vac heaters
5.3 Amps
.06 ohms
1.6 Watts dissipated
ijedouglas wrote: ↑Sun Oct 01, 2023 4:36 pm
How does it sound?
It sounds great to my uneducated ear, better than any other amp I have, already. I still need to bring the bias up and set the PI balance and OD level. I messed with the FET level a little.
All said I REALLY like it! Can't wait to hear what the power tubes sound like
GAStan wrote: ↑Sat Sep 30, 2023 7:12 pm
Got our 2x12 and plugged it in. VERY quiet now, hiss is gone! Now it reacts as I expected it to, a bit of hiss and slight hum variable with volume controls and swithces. Right now the heater circuit is disconnected and my meter is completing it so some 60 cycle hum is expected. This is all with nothing plugged into the input or effects loop. Gonna let it burn in more and when I get a chance plug in a guitar.
Sounds like progress. Something you might try now, if you want to keep the noise down, is to hook up a radio station on the input and run the amp on the dummy load.
Still looking for a sound source. I'll break out a signal generator and o'scope later today.
Yet another mistake. The PreAmp Boost and OD switches operate opposite the chassis markings. I just wired them according to the layout which is for SLIDE switches. This chassis takes TOGGLE switches. Where's the facepalm emoji?
Finally tried out the footswitch. It works as it should once the chassis switches are in the correct position.
I WILL correct the switches.
As you have probably figured out I have no shame nor pride of the self inflating kind. Hopefully posting about my mistakes not only amuses the experienced but also helps prevent someone from repeating them in the future.
GAStan wrote: ↑Sun Oct 01, 2023 8:45 pm
I just wired them according to the layout which is for SLIDE switches. This chassis takes TOGGLE switches. Where's the facepalm emoji?
As you have probably figured out I have no shame nor pride of the self inflating kind. Hopefully posting about my mistakes not only amuses the experienced but also helps prevent someone from repeating them in the future.
Which layout do you use? #124 layout is toggle switch?
We all make mistakes, in my case one was particular very cost ineffective. Designing a fet board with a fault. Selling them, then contact all buyers on the fault and sent the correct ones for free. m-)
GAStan wrote: ↑Sun Oct 01, 2023 8:45 pm
I just wired them according to the layout which is for SLIDE switches. This chassis takes TOGGLE switches. Where's the facepalm emoji?
As you have probably figured out I have no shame nor pride of the self inflating kind. Hopefully posting about my mistakes not only amuses the experienced but also helps prevent someone from repeating them in the future.
Which layout do you use? #124 layout is toggle switch?
We all make mistakes, in my case one was particular very cost ineffective. Designing a fet board with a fault. Selling them, then contact all buyers on the fault and sent the correct ones for free. m-)
Erwin, I do not have any issue with the chassis you make it is not specifically a 124 chassis. Yes I made a mistake, it was my mistake. However #124 does have slide switches in the rear for OD and PAB.
ODS_124090.jpg
The layout is for these slide switches, not toggle. The front switches are toggle and the layout reflects this.
Erwin you provided a GREAT chassis and I highly recommend it. The fact you made right on the FET boards shows you are an honorable person to do business with
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GAStan wrote: ↑Sun Oct 01, 2023 8:45 pm
I just wired them according to the layout which is for SLIDE switches. This chassis takes TOGGLE switches. Where's the facepalm emoji?
As you have probably figured out I have no shame nor pride of the self inflating kind. Hopefully posting about my mistakes not only amuses the experienced but also helps prevent someone from repeating them in the future.
Which layout do you use? #124 layout is toggle switch?
We all make mistakes, in my case one was particular very cost ineffective. Designing a fet board with a fault. Selling them, then contact all buyers on the fault and sent the correct ones for free. m-)
Erwin, I do not have any issue with the chassis you make it is not specifically a 124 chassis. Yes I made a mistake, it was my mistake. However #124 does have slide switches in the rear for OD and PAB.
ODS_124090.jpg
The layout is for these slide switches, not toggle. The front switches are toggle and the layout reflects this.
Erwin you provided a GREAT chassis and I highly recommend it. The fact you made right on the FET boards shows you are an honorable person to do business with
I see , slide on back, toggle on front. Some many variables on different generations chassis.
Thanks for your kind words.
. Took 115 vac into amp to get 6.3 vac heater supply. 125 vac wall voltage gives 6.8 vac @ 5.5 amps.
