Marshall 1959rr no play with Fryette power station

[The Dude]

Are load settings properly matched both amp to power station and power station to speaker?

[tdlunsfo]

This would be a 16ohm resistor. Bias Current is one of those inline socket adapters that puts your ammeter between the plate and B+. So I guess "plate current" instead of "bias".

Also I wasn't setting bias above but simply testing different parameters while under load. The amp bypassed was around 65w, same settings through the PS-2. If you all want idle current, I can supply it.

[tdlunsfo]

Are load settings properly matched both amp to power station and power station to speaker?

Everything is set to 16 ohms on both amp, PS2 and dummy load.

[tdlunsfo]

Idle plate current is 30mA at 448v. 54% dissipation.

[tdlunsfo]

Are the number per valve or for more than one valve?

Only have numbers for one tube currently. Let me know if there is something specific that would help. I have another bias probe and this amp has the 1 ohm current sense resistors.

[g1]

Is the dummy load part of the power station working? What does it read for a load when NOT bypassed?
I see lack of tube current and blown screen resistors and think unloaded amp (or too high load impedance).

[The Dude]

While playing I did get some slight noise on the waveform but it never went into full blown oscillation. I was actually measuring bias current/ voltage, B+, screen while testing on the dummy load, here are the numbers:

B+: 398
Screen; 311
Bias Current: 4mA
Bias Voltage: -45

Same amp settings but Power Station bypassed:

B+: 356
Screen; 326
Bias Current: 92mA
Bias Voltage: -42

4mA is not a typo above. I checked muliple tubes and same. I chalked it up to something the power station was doing.

The power station should present the same load to the amp whether bypassed or connected. The internal 16 ohm load should (theoretically) be the same as the speaker when the unit is bypassed. I would check the load with your meter both connected and bypassed and verify it is the same or similar.

[tdlunsfo]

Is the dummy load part of the power station working? What does it read for a load when NOT bypassed?
I see lack of tube current and blown screen resistors and think unloaded amp (or too high load impedance).

It's a little unclear to me how to test to make sure it's working correctly. I guess I can hook an ohmmeter up to the amp in jack on the back of the power station to see what it reads.

[Chuck H]

It's a little unclear to me how to test to make sure it's working correctly. I guess I can hook an ohmmeter up to the amp in jack on the back of the power station to see what it reads.

Yes. And wiggle things around when you do that to see if there are any intermittent faults in the connections. And...

Above you show voltages with the Power Station in the circuit and then bypassed. Are these voltages measured while the amp is conducting signal? They don't make any sense to me. Nothing about the Power Station should cause the plate voltage to rise and the screen voltage to drop. Please recheck those numbers to confirm that your plate and screen voltages are indeed different ONLY with the Pwer Station in the circuit WITHOUT the amp conducting signal.

EDIT: Another possibility... I'm recalling a build I did some years ago where I couldn't seem to find EL34's that would hold up in rather vanilla circuit. Screens kept popping. I went through three pairs before one finally held up. I had purchased two different pairs from a vendor I will no longer use (both JJ but of different suffixes) and one pair from Ruby. As far as I can tell to this day the problem was poorly tested new tubes that were faulty as the last tubes to go in (the Ruby's) are still in the amp and working fine years later. Just illustrating that coincidences like this can happen.

[pdf64]

While playing I did get some slight noise on the waveform but it never went into full blown oscillation. I was actually measuring bias current/ voltage, B+, screen while testing on the dummy load, here are the numbers:

B+: 398
Screen; 311
Bias Current: 4mA
Bias Voltage: -45

Same amp settings but Power Station bypassed:

B+: 356
Screen; 326
Bias Current: 92mA
Bias Voltage: -42

4mA is not a typo above. I checked muliple tubes and same. I chalked it up to something the power station was doing.

Are the numbers whilst the amp is idling, or with it passing audio?
If idling, was it checked for ultrasonic oscillation whilst in that mode, with those loads?
If idling, could the test be repeated but with the valve in V3 LTP phase splitter removed? (That should eliminate the ability of the output stage to oscillate).

[Chuck H]

Yep. This. Helmholtz called out the possibility of oscillation back in post 5 and I haven't seen it clearly addressed yet.

Maybe I don't have enough experience with this but I don't understand how oscillation would cause the plate voltage to rise while the screen voltage drops and measured current through the tubes to drop to almost nothing. The results in that test seem too weird to be anything but a failing tube.?.

[tdlunsfo]

Yes. And wiggle things around when you do that to see if there are any intermittent faults in the connections. And...

Above you show voltages with the Power Station in the circuit and then bypassed. Are these voltages measured while the amp is conducting signal? They don't make any sense to me. Nothing about the Power Station should cause the plate voltage to rise and the screen voltage to drop. Please recheck those numbers to confirm that your plate and screen voltages are indeed different ONLY with the Pwer Station in the circuit WITHOUT the amp conducting signal.

EDIT: Another possibility... I'm recalling a build I did some years ago where I couldn't seem to find EL34's that would hold up in rather vanilla circuit. Screens kept popping. I went through three pairs before one finally held up. I had purchased two different pairs from a vendor I will no longer use (both JJ but of different suffixes) and one pair from Ruby. As far as I can tell to this day the problem was poorly tested new tubes that were faulty as the last tubes to go in (the Ruby's) are still in the amp and working fine years later. Just illustrating that coincidences like this can happen.

The amp in jack on the Power Station measures 870 ohms. The numbers above are with a 500hz audio signal going into amp and the power station connected to a 16 ohm resistor. My scope connects to my resistor box and I have never had the amp go into HV oscillation. The amp was running around 65W bypassed in this setup (second set of readings). The first set of readings are with the power station in operate mode.

[Greg Robinson]

The amp in jack on the Power Station measures 870 ohms.

That's definitely suspicious. Seems like the Fryette power station has a faulty reactive load.

[Chuck H]

That's definitely suspicious. Seems like the Fryette power station has a faulty reactive load.

Agree.

[tdlunsfo]

I'm in touch with Fryette tech support now, and I'll post back here what they suggest. Agree 870ohms seems off, but was verified on two different meters.