On the hunt.
WHYG?
1 Like
I bought some psvane Tii mk2 for a line magnetic amp and pretty sure I put the LM ones back in and kept the psvanes when I sold it.
I’ll have a look for them tomorrow and if I can find them I’d sell them for £150 +postage
2 Likes
How many have you got Chris?
1 Like
a matched pair
2 Likes
That might work out well. My amp uses 4 but 2 are voltage regulators. Just waiting on a reply from Guy to see if I need to change those as well.
Ill take the 2 youve got though.
1 Like
A Viva Solista?
1 Like
It is.
I’ve always found these to work fine & sound good in my Solista. And they’re not too dear.
4 Likes
My experience with Viva 845 amps is that they go through valves. I think the designs run them at a very high voltage, apparently to get the very best sound. I think the Shuguang are the standard issue and in my experience lasted the longest. I don’t remember if the Solista was too bad in this respect, but the monos I had ate tubes, to the extent I had the voltages adjusted. Great sounding amp though, the Solista.
Cheers Ritchie
I’ve had it a few years now and it’s going strong on the valves that came with it. Unknown hours etc.
It’s had plenty of use at that too so I’m hopeful it will carry on behaving.
It occured to me last night that if one does fail, I’ve not got known spares.
I did get a couple wiyh it but I don’t know anything about them.
1 Like
They seem to be using one of the pairs as a full wave rectifier although I’m not sure which pair it is without seeing an internal shot. I’m also not sure how using them as rectifiers affects those valves’ longevity or respectively how their ageing would compromise performance as opposed to the ageing of the SE output stage. @Valvebloke , any thoughts?
It’s 16-17 years since I had a Solista, but I think the output valves are the rear ones. 
“The Solista MkIII is a full Class A single-ended triode design running four massive 845 tubes; the front pair acts as hybrid rectification power supplies, and the rears do output duties.”
4 Likes
I’ve no first hand experience of strapping triodes as rectfiers I’m afraid. I can speculate though:
Assuming no catastrophic accident or appearance of gas, power valves tend to fail by loss of cathode (filament) emission and that’s caused simply by current flow over time. In a stereo SET amp each rectifier will be handling roughly the same average current as each output valve. Whether the peak currents differ greatly (peak current can also see your valve off) will depend on the power supply design. If it’s capacitor-input (particularly if it’s what the military once called CFE- ‘Capacitor, F**king Enormous’) then the rectifier waveform will be spiky and the rectifier’s peak current might well be a problem. If it’s choke-input then the rectifier waveform will be much smoother. Now the rectifier will still be working a bit harder than the output valve, but perhaps not significantly. I don’t know if the Solista is cap-input or choke-input. Great-big-triode amps need lots of HT voltage - often north of a kilovolt - and it’s easier to get that voltage with a cap-input psu. Also a great big choke is expensive and heavy and it needs an assured load current too, which often involves a wasteful hot wirewound resistor, all of might well put the designers off choke-input. Then again, Border Patrol supplies work that way and they seem popular.
Another difference is that rectifiers see a large reverse voltage for half of each cycle whereas output valves don’t. I suppose that might increase the risk of some sort of rectifier breakdown, but as long as the breakdown doesn’t actually happen it shouldn’t affect the life much (could emission from a hot grid back to the cathode be an issue though ?).
Ritchie says the rectifier scheme is hybrid which I take to mean that there are two valve diodes and two solid-state ones. The obvious way to connect these would be as a hybrid bridge. This would be kinder to the power transformer. Otherwise the thermionic diodes could be set up in an FW scheme with an SS diode in series with each one as an insurance policy, and perhaps also to drop most of any reverse voltage. These two schemes are quite different but I’m not sure that they’d result in different rectifier lifetimes.
Long story short, a triode strapped as a rectifier will always be working harder than one used as an output valve, but whether it’s sufficiently harder to shorten the life probably depends more on the details of the design rather than the fundamental principle.
4 Likes