A kit similar to the original WAD 300B Stereo PP?

Originally Posted by Paul Barker

I can't see my category on the vote so have to publish reply. I prefer Greg and co's to the pp pentode amps. 300b's are quite cheap these days, you don't have to buy the boutique ones to get reasonable sound.
The valve itself helps to get a sound out of push pull which is closer to SE. It's a good blend of compromises, the parallel 300b se doesn't seem to sound right. The market for a SE single 300b can't be ignored either but yes I vote for another look at this type of pp amp.
The voltages are relative, if you are talking about valve amps shut up about voltage.

Paul, thanks for clarifying in another thread what you mean about voltages, I agree with your point in it that offering kits with kV+ HT is dangerous.

I mentioned the 0.56kV HT of the old WAD 300B PP in my Poll options because, to the best of my knowledge, this was the highest voltage ever used on any of the WAD kits. I'm not sure if that is too high these days for liability insurance?!

Valve amplifier kits will always require voltages even if we "shut up" about them, I liked the way that Nick pointed out their direct influence on SE output power in that other thread.
Lots of people want (relatively) lots of Watts from either their preferred topology or their first 'valve amp.'. Awareness of the voltage consequences are better out in the open, especially in a forum that welcomes all from the highly experienced to the novice.

You and I clearly agree that big voltages are dangerous, but where should WD draw the line for a commercial kit: 565v; 750v; 1000v; 320v?
To my mind, the answer to this question will give us all an idea as to the type of kits that can be offered by our new hosts.
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[Paul Barker]

Yes I used my usual technique of punchy remarks to spice the reply, but which are easily read differently.

I don't think the pp300b voltage is an issue, but as I said before about the Chinease 845 amps maybe a year ago, I didn't think it was a great idea for a beginner to start at these voltages with suspect kit. Now maybe the Chinease 845 amps are of sufficient build quality as it now turns out, but I have yet to receive Ian's and find out what is causing fuses to blow.

We all have an idea where we think the line should be drawn. I think the line stops at the 300b for single ended power mungers because to find any more power from se means much higher voltages. You can get the same power as a 300b with the same voltages but not more.

My objection to the 300b per se so many years ago now was based on the extortionate price of the bottle, now that market forces have levelled that, it's a good value for money product. Not as good a value as the Sovtek 2a3 or the nos 6b4g, but they aren't in the same power class.

To achieve power and keep below the kilowatt a push pull 300b amp is the most sensible.

[dave dove]

or you could use next gen 300b

vv30 or 300bxls or similar

just keep HT the same
and increase current
they really do like it

dave dove

[NickG]

From a safety point of view one option using a transformer to couple to the final stage does give you, is the potential to use a split rail for the final stage. The only downside I can see is you need a extra choke in the power supply and maybe a bit more complexity in the power supply, but it does mean a 1kv output stage coule be built without more than 500v to ground at any point. One hand on the anode and one on the cathode would still be a bad thing though. A 845 at 800v could be done, using 500v caps for example, that should give about 17w of output, and there are the nice metal 845's about now.

Paul,
As one guilty of a 'spicy reply' or two myself I know where you're coming from.
The points you made just above are good and I'd concur that the 300B PP voltage was about as high as you would want to go in a kit.
Which would disappoint those wanting a 211/845 big-watted SE until Nick's split-rail suggestion!

[Les Reed]

Originally Posted by NickG

From a safety point of view one option using a transformer to couple to the final stage does give you, is the potential to use a split rail for the final stage. The only downside I can see is you need a extra choke in the power supply and maybe a bit more complexity in the power supply, but it does mean a 1kv output stage coule be built without more than 500v to ground at any point.

The problem isn't just about bare voltage, but also the huge amount of energy stored in the PS capacitors. I wouldn't like to be anywhere near 100-200uF with 500V on it.

With regard to an upper voltage limit for valve kits, the EEC low voltage directive goes up to 600V. So anything above that is covered by the high voltage directive, which is much more stringent. Whether this is relevant to a supplier of bare components, machined metalwork and a list of build intructions, I don't know.

[NickG]

Bear in mind I have always argued that high voltage kits are a bad idea, so this is just for discussion sake...

I wouldn't like to be anywhere near 100-200uF with 500V on it

Agreed, I certainly wouldn't like to be near it when it was shorted to earth, but thats exactly what you have in the WAD kit6550 amplifier, and that was sold without problem

I assumed that 600v was a limit, as thats a common max voltage for multimeters. Again though, the 6550 had a 425-0-425 transformer, which we would call a center tapped 850v TX if we were talking to a winder. So that begs the question is the 600v limit a limit to ground, or from any point in the circuit to any other point?

Thinking about it, the 6550 transformer would make a passable 1100v CT power supply. Thinking more, if the WAD 300b transformer had just a little more current on its 5v lines, it could be used to make a nice little transmitting triode monoblock amp, the 1000v CT B+, -100v for a bias supply, and almost enough to give 10v @3a for the heater. Or the 100-0-100 could be used to power a driver stage.

Just lazy Sunday musings though.

Whether this is relevant to a supplier of bare components

I would guess not, I have never had of a problem ordering 3k CT (for example) transformers from ECC suppliers.

[Richard]

The polling cats don't suit me either.

Yes the old 300BPP is good.

No it isn't the best for all people and shouldn't be maketed as a "flagship" to aspire to.

Any idea of trying to establish a "hierarchy" of amps is daft as people all have their own needs and budgets and good sound exists for all these. Imho WD need to offer a large range and revisit old designs regularly rather than the old WAD policy which resulted in a shrunken range and many babies thrown out with the bathwater.

Doesn't it strike anyone as odd that they never offered a 300BSE??

Rich

[NickG]

Well they almost did have a 300bSE, but it never made it to sale :-(

[Paul Barker]

When I talked to Mark at Eggfest he expressed conscern that the SE300b they had prototyped sounded better than the 300b pse. He couldn't seem to accept that was the way of things, and was talking in termns of a hierachy where the 300b pse had to be better. Whether that is relevant to why the product se 300b didn't appear noone can tell, there are so many factors to overcome in bringing kit to market.

THere will always be folk who prefer parallel 300b others single and yet others PP.

I think two products in the 300b line up, PP and single would sell. A single 2a3 amp, a kel84 and a kit88/6550 amp.