NOSValves

I can tell you from first hand knowledge never underestimate how gullible people can be when dealing with something new to them.

A couple technical reason for this... 1) A power amp has no break or throttle... when its on its ready to amplify to its full ability any signal presented to it..preamps can and do often makes strange electrical noises as they come up. 2) all electronic devices with capacitors are unstable when first turned on. The capacitors leak DC voltage while the B+ is unstable for the first few seconds after turn on. This will send a small amount of unstable dc voltage to the amplifier which not catastrophic but I'd advice against it since it's easily avoided. The above is true of SS or tube gear.

Yup probably oxidized sockets and tube pins!

Hey sometimes I get lucky! Glad you are back up and running!

Do the tube heaters still light up? If so you probably blew the very first cement wire wound resistor in the B+ directly connected to the 5AR4 rectifier output. If the heaters don't light up the amp is not getting power for some reason. Check that fuse for continuity with a meter. Those old original slo blo fuses can blow but not show obvious visual signs of it. If the amp is still original it's long past the time it should have been restored so yes I'd suggest getting it properly rebuilt.

One of the best from the vintage era!

Have ever tried dumping the bridge configuration and just run one of those Decwares? I myself have never been a fan of bridging two channel together...

looks pretty scary to me... Here is what they look like before the creative rebuild

I bet the Decware is much easier to listen too for hours on end. What Decware exactly are you using that is 5 watts? I thought the EL84 triode amps they produced were less than 3 WPC ?

nothing wrong with giving a little console pull for a taste of tubes on the cheap. Just temper your expectation its a taste not the full meal.

I'll third that.

rough crowd... while I'll not defend his very liberal way using parts PWK designs in his speakers. His speakers are different in many important ways to the stock klipsch designs. IMHO his big mistake that ruffled so may feathers is the way he trashed the hand that fed him in some ways...

I agree but he'd have to find a pretty beat up used pair to score them within his budget.

Oh and as to what I meant by user error. Its pretty easy to screw up the biasing if the amps has a control per channel to balance the pairs of tubes and the technician added a control feeding each balance control to raise and lower both tubes in the channel at once. Here how the error would happen. I'm assuming the bias scheme was setup keeping the factory bias balance controls in the circuit. You insert both probes in the test points for the channel to be balanced and set the balance control so your meter reads 0 VDC (zero equates to both tube being the same), Then you pull the black probe out place it on the bare chassis for ground and check the bias voltage (here is where the mistake comes in) mistakenly you adjust the balance control instead of the new bias voltage control to lower the tube the red probe is inserted in. The balance control can lower one tube but in doing so raises the bias of the other tube in the channel. If this is allow to run for a few hours that tube that is mistakenly biased high can decide to red plate from long term over bias condition.

Well realize I'm to some degree guessing so don't take my comments as written in stone. It's pretty much impossible to consistently diagnose these problem over a forum. Most of my guessing that led me to say user error is amps that are red plating don't sit for a day or two then just stop red plating. These types of things don't magically fix themselves. The only thing that comes to mind that could make this intermittent would be tube pin to tube socket connection problems (as is loose dirty sockets). I'd be watching it close until the problem gets tracked down for sure.