New issues on my JTM45 build while testing tubes.

[gtrplayr1976]

Now what's the good reading? Do you need further advice?

It's at 390 VDC after initial startup. It runs over 500VDC on startup. The thing I'm trying to find now is that when I take it off standby I can hear a faint puttering until the bias mA reading on the probe/meter reaches about 27-29mA. I just tried jumping the standby switch to see if that was a cause ,but it did the same thing.

[Helmholtz]

It's at 390 VDC after initial startup. It runs over 500VDC on startup. The thing I'm trying to find now is that when I take it off standby I can hear a faint puttering until the bias mA reading on the probe/meter reaches about 27-29mA. I just tried jumping the standby switch to see if that was a cause ,but it did the same thing.

390V PI supply voltage seems very high. What is your heater voltage? (sorry if you already posted it somewhere). Some voltage overshoot before all heaters are hot is normal, but 500V is extreme. A tube rectifier should reduce the overshoot as its own heater delays voltage build-up.

[gtrplayr1976]

390V PI supply voltage seems very high. What is your heater voltage? (sorry if you already posted it somewhere). Some voltage overshoot before all heaters are hot is normal, but 500V is extreme. A tube rectifier should reduce the overshoot as its own heater delays voltage build-up.

The PI supply voltage on a Bassman is 385 ,so I figured this would be within spec since it is very similar?

Heater voltage is 6.5VAC. I am using a copper top from Weber for the rectifier ,but I am going to order an actual GZ34/5AR4 to see if there's a difference.

[Helmholtz]

The PI supply voltage on a Bassman is 385 ,so I figured this would be within spec since it is very similar?

True, but the 5F6-A has a lower value dropper resistor (4.7k instead of 8.2k in the JTM45). Nothing wrong with 390V but on the high side for a JTM45. Does your PT have a 240V mains input tap? If available I often use the 240V tap when voltages are high.

[gtrplayr1976]

True, but the 5F6-A has a lower value dropper resistor (4.7k instead of 8.2k in the JTM45). Nothing wrong with 390V but on the high side for a JTM45. Does your PT have a 240V mains input tap? If available I often use the 240V tap when voltages are high.

It does have a 240 tap ,but is that safe to use with 125v supply ? I've never heard of this being done?

[Helmholtz]

It does have a 240 tap ,but is that safe to use with 125v supply ? I've never heard of this being done?

Sorry, I goofed. Thought you were in Europe. Our nominal voltage is 230V and import PTs or amps often are designed for 220V. So at 230V internal voltages are too high and I switch to the 240V tap if available. So you would want something like a 130V tap.

Using the 240V tap with 125V input would be safe but give very low amp voltages.


BTW, what does WV mean?

[gtrplayr1976]

Sorry, I goofed. Thought you were in Europe. Our nominal voltage is 230V and import PTs or amps often are designed for 220V. So at 230V internal voltages are too high and I switch to the 240V tap if available. So you would want something like a 130V tap.

Yeah there's no tap for that.

BTW, what does WV mean?

LOL...West Virginia United States.

[Helmholtz]

Thanks. We also abbreviate our federal states, like BY, BW, NRW, RLP etc. Of course I don't expect foreigners to know.

[gtrplayr1976]

Thanks. We also abbreviate our federal states, like BY, BW, NRW, RLP etc. Of course I don't expect foreigners to know.

Germany is one of the places I would love to visit especially the old places.

[gtrplayr1976]

Sorry, I goofed. Thought you were in Europe. Our nominal voltage is 230V and import PTs or amps often are designed for 220V. So at 230V internal voltages are too high and I switch to the 240V tap if available. So you would want something like a 130V tap.

Using the 240V tap with 125V input would be safe but give very low amp voltages.

What does this sound like to you? It is there at startup when it reaches a certain voltage, and/or bias mA reading. Cap? Well crap, for some reason the mp4 file won't upload. Have to try something different. Hopefully this will work.

https://www.youtube.com/watch?v=iBYq...ature=youtu.be

[Helmholtz]

What does this sound like to you? It is there at startup when it reaches a certain voltage, and/or bias mA reading. Cap? Well crap, for some reason the mp4 file won't upload. Have to try something different. Hopefully this will work.

https://www.youtube.com/watch?v=iBYq...ature=youtu.be

Never heard something like that with an amp. Sounds like a motorcycle. Is this with a GZ34? Are your filter caps rated at 500V or higher?

[gtrplayr1976]

Never heard something like that with an amp. Sounds like a motorcycle. Is this with a GZ34? Are your filter caps rated at 500V or higher?

Cans are 500v. I don't have a GZ34 tube yet. I have ordered some. Using the Weber coppertop right now. Well "motorboating" is a sign of bad filter caps ,but it usually continues ,and doesn't stop like this does ,so I'm not sure either.

[Helmholtz]

Well "motorboating" is a sign of bad filter caps ,but it usually continues ,and doesn't stop like this does ,so I'm not sure either.

True and motorboating typically sounds different. Let's see if its still there with the GZ34. You might even use a 5U4GB for a little lower voltages if your PT supports the higher heater current.

[gtrplayr1976]

True and motorboating typically sounds different. Let's see if its still there with the GZ34. You might even use a 5U4GB for a little lower voltages if your PT supports the higher heater current.

Should get the GZ early in the week. 5U4GB won't work. PT only handles 2A. I was going to do that a long time ago.

[pdf64]

I seem to remember having a 12AX7 that made that quiet motorboat noise, try subbing out each in turn with a good one.