Fryette 2/90/2 Multimeter & Fuse Type

Power Amps 2/90/2
1

Hello,

I have a few general technical questions regarding the Fryette 2/90/2. Channel B blew a fuse, which I presume was due to an older blown power tube, as I heard a classic pop followed by no output from that channel. Channel A is still working perfectly normal.

  • When using a handheld multimeter, what is the minimum voltage specification required to bias this amp across the fuse terminals? I assume a higher multimeter spec for safety, such as 1000V, since the plate voltage on the 2/90/2 high power mode is approximately 700V?

  • The fuses I pulled out of this amp were 1 1/4" @ 1A / 250V, is this correct? Fast or slow blow? (bottom one pictured is the one that blew)

  • Tube types in Channel A and Channel B can be different as long as they are biased properly? For example, Channel A can use KT88s while Channel B can use 6550s?

Thanks kindly everyone for your time and help. I look forward to having this amazing amplifier repaired and back in working order!

zewo83R1gJRSM3a2
zewo83R1gJRSM3a21118×1033 140 KB

2

Hey Scorpius, welcome to the forum and thank you for your question.

  1. Actually, you will measure Current, rather than Voltage across the fuse terminals. Milliamps to be exact.

  2. That’s correct.

  3. Yes. That’s correct.

See biasing instructions here:

2902Bias.pdf (50.2 KB)

1 Like
3

Thanks, @DavidPhelge I really appreciate your response. I just want to clarify a couple of points here for absolute certainty.

Regarding the multimeter, and I apologize if I misunderstood, do I need to use one with a higher safety rating (e.g., 1000V), or will any multimeter that can measure milliamps suffice? I am accustomed to working on amplifiers with lower plate voltages, so safety is my top priority.

Thank you for confirming about the fuse rating. Are they fast acting or slow-blow?