NOSValves

The cold to hot cycle is hard on tube equipment and the tubes themselves...but you also have to weigh in the fact that every hour on is an hour of life used up on the tubes....my rule that has served me well in my shop system is I turn it on when I first enter my shop for the day and turn it off when I'm done for the day. Thoughout the day I might not actual play music for multiple hours out of the day. But I personally still prefer one cold to hot cycle a day. Using this approach has my current VRDs I built way back in 2003 running 14 to 18 hours most days without failure. I often get 7000+ hours out of a set of output tubes and retire at that point because they start to show unstable bias. I've to date never had an output outright fail. I have lost a few used Mullard 5AR4's over the years.. So I suggest turning your tube gear on once a day about 20 minutes before your going use it and then off when you know your done using for the day.

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.

The upgraded transformers is when comparing them to regular ST70 transformers. The Latino ST120 utilizes larger transformers to better take advantage of the use of KT88 output tubes rather than EL34 which is what the ST70 is optimized to use.

stuffed with Auricaps.......that is one heck of a good deal.

Well honestly I wonder if this is user error. Not sure how they setup your biasing scheme but if they kept the balance controls and added voltage controls like I do to a 222C I've had a few folks get confused and mess up the bias. Reason I suspect user error is things like this don't generally fix themselves in my experience.

Ahh okay I just reread your first post.. those vintage Siemen EL84's should have been fine in there...if they were good to start with. The only real problem with running regular EL84's in the amplifier designed for 7189's is they will not last long, they generally run just fine and sound really good. They just don't last as long. Vintage EL84's hold up better to this abuse then most modern productions. Thing is in my opinion those Russian surplus tubes (preferred series) and the current Sovtek EL84M (same basic tube) sound really good and last like any 7189 ever made. PS: one of the reasons those EL84's sound so good IMHO is you're running the dog shite out of them!

What do you mean by "you put the wrong tubes in it" ? I'd suggest taking it into your technician something is bad and it is almost surely what caused the tube to red plate in the first place. It happens and probably will be a easy fix. If the filter can directly in front of the power transformer is original I suspect that will have something to do with it.

Do the tubes seem to have a good bit a tension putting them in and pulling them out of the tube sockets? You may have intermittent tube pin contact going on. If the control grid doesn't achieve good contact the tube will run away cherry red. I take the amplifier was modified to allow you to test tha adjust the bias since the original 222C only came with balance controls and no provision for testing the bias.

The bulshite is worth the dizziness..

Passives don't achieve it either!

Actually no they are never 100% out of the circuit they always add a resistive path to ground...