I have a problem with my Fryette Deliverance 120 Amp. Half a year ago, the DC fuse blew. A KT88 power tube was defective. After that, I installed a completely new set of tubes and biased them (EH KT88 power amp). Now the amp is starting to make noises again. It hisses and pops occasionally, and it sounds like it’s rattling. You can hear this through the speaker.
Does anyone know what could be causing this?
I actually wanted to replace the filter capacitors, but I can’t get the right size ones here in Germany.
See here, What 6550s do you recommend? Steve mentioned that sometimes 6550 (KT88) have these noises, but that they get burnt out.
You could try burning them in a bit longer. But otherwise, you could arrange a service. Could you tell me if your D120 was purchased new and is still in warranty? Or is it out of warrant?
Hello!
Thanks for the feedback. No, the amp is no longer under warranty. I’m the first owner, but the amp is from 2009 (old model, without choke).
I’m afraid the tubes are defective. I set the tubes to 60mA six months ago. I checked everything again after a few hours. Today I measured the bias and it’s V6=78mA, V7=74mA, V8=29mA, and V9=35mA. The bias has drifted considerably.
I checked the voltages at sockets V6-V9 again without the power tubes. The values actually look good?!
Pins 2+7 = 6.3V (AC)
Pin 3 = 464V
Pin 4 = 457V
Pin 5 = -38V
I’ll probably get a set of TAD or JJ 6550 tubes and replace them.
You have to be aware that the spec sheets and what makers of things like the Bias Probe for example advise, is only useful in explaining general concepts and do not take into account actual operating conditions in specific designs, like line voltage, specific plate voltage and how that voltage changes with the bias setting, etc. That’s all conditional info.
My advice here is specific to this amplifiers design and operation and based on 120V/240V AC line voltage.
