EL34 PP Amp

[NickG]

The problem with a universal amp is less the bias, and more B+ and transformer. You may end up with a amp that doesn't get the best from any of the valves.

[Clive]

I was thinking what's needed is a mains tx with 2 B+ windings, one for EL34 and the other for 6550/88. There could be 2 options for opts so you choose the opt when buying the kit. This should enable optimised op points. The heaters are close enough in current consumption to be ok.

WAD considered 'Swiss Army Knife' aka 'Jack Of All Trades' amplifiers with switchable this, that and the other and decided that they would create too many support issues.
"I have input option A, using valve option 3, it doesn't work - help", etc, etc, etc, etceteras!

As Nick implies, design a good and optimised kit instead of trying to offer some kind of half way house.

[Rupert]

Glad to see there are a few fans of the old Kit34, it was rather over shadowed by the 6550 and I've often wondered if this was fair. It was Nick Lucas who persuaded me to choose it over the 6550. Said if I wanted something a bit different sounding, something clearly valvey and obviously not SS (which is probably not uncommon amongst those considering a valve amp), with some character it would be the one to go for. The difference in cost was entirely down to the valves as the circuit is almost identical.

I think it sounds good (better with some tweaking of course) but I've not heard a 6550, and often wonder if I made the right choice. It sounds particularly fine, in fact amazing, with guitar based rock, which is a particular weakness of mine. Seems to like being cranked up though, not so exciting at low levels. Brass and big fat 80s synths also come over rather well.

Perhaps I should change the cathode bias and stick some 6550s in it one day, or would I be wasting my money?

Rupert

[Clive]

I don't understand this halfway house stuff for a 34/6550/88 amp, the differences are really very, very trivial. This is not a universal amp, it's one that can run 3 output valve types that have not very differing requirements. The Kit34 and Kit6550 were virtually the same! The Kit34 can even use 6550's and 88's without modification.

I'm not suggesting an amp that'll run 300B and 6550.

If costs can be shared between 3 versions of an amp then overall costs will be lower. This is not rocket science, it's just a more effective way to reduce costs but still allow for 3 output valve types to be used in an optimal way.

[NickG]

The biggest difference is the max screen voltage for the el34. That does present a restriction for the 6550 and kt88 in terms of B+ for a UL amp.

[Clive]

Originally Posted by NickG

The biggest difference is the max screen voltage for the el34. That does present a restriction for the 6550 and kt88 in terms of B+ for a UL amp.

Which is why I suggested using a main tx with 2 sets of B+ windings (or more likley an extra set of taps). It is of course possible to offer 2 different mains tx's but having a single tx wound in greater volume should be cost beneficial.

Diyhifsupply use a mains tx like this as it has some boost/buck windings too. I wouldn't advocate a tx that could be used for any amp, there would be too many extra wires.

Along with offering the correct opts for whatever the customer choses for the output valves then the other changes are down to a few resistors.

This would give benefits for product development and parts sourcing, same chassis too.

Marketing is a different matter, the amps could be offered as 3 different part numbers or one base part number with an option to select the parts pack for the chosen output valve.

[FlyingKipper]

Kat34 was my first self build amp, so I would reccommend something similar is offered. For me it was more attractive than the 6550 equivalent because it was about £100 cheaper! oh yes..... and it didn't have such a reputation for a vibrating mains TX!