recommended Output TX's for PT15 ?

[Corne]

...settling on Va=600V, Ia=50mA or 60mA and Vg=-70V as a nice OPT - with an 8K OPT setting it looks like 7 to 8 watts output.

James,

If you enter 8k load at cell U67 of the spreadsheet and then enter 50mA and 60mA you'll see that at 50mA you'll have more power output than at 60mA. So running more bias current doesn't always mean more power output.

Corne

[James D]

Hello Corne,

Yes, I found that out late last night with your model. It really is excellent The realtionship between load impedance, op. point and power output is beautifully illustrated in your model. In particular it shows how the optimum load impedance is actually quite sensitive to Ia. I like the indication of THD that you get through comparing Va(max) and Va(min) as well.

It really is a super piece of work and I really appreciate your publishing it.

Many thanks

James

[Corne]

James,

The difference in Va(min) and Va(max) is not an indicator for THD.
I'm using Va(min) and Va(max) to calculate the maximum power before clipping for the positive and negative part of a sine wave. The maximum output power without clipping is equal to the lowest value of these two power calculations.
If the voltages are almost identical that means that the bias point is well centred, indicating an optimum load for a given bias.
If the load resistance is to low for optimum power output at a given bias the power output is limited by I^2*Rload. If the load resistance is to high then it's limited by the minimum voltage drop over the output valve, Vg=0 curve. This gives the distinct peak in the power output graph on the bottom right.

Corne

[NickG]

But does that not also give a indication of the amount of 2nd harmonic produced?

I should look at this spredsheat, it sounds great, and I wonder if the method shown in this page could be added to give am idea of the harmonics created

http://members.aol.com/sbench102/po-dis.html

[Corne]

It's not an indicator for THD because I'm only using the Vg=0 curve to determine maximum power output without clipping. The THD can only be calculated if more Vg curves are used, the distortion calculation on Steve Bench's site uses five.
Unfortunately the PT15 data on Pete Millett's site only goes to 400V so THD calculations for higher voltages isn't possible and the PT15 likes to be run above 400V. That's why there isn't a THD calculation in my spreadsheet.

Corne

[IslandPink]

Guys,

Any preference for CV1104 or PT15 if both are available ? Brands ?

MJ

[Corne]

I'm not aware that there are any differences between PT15,CV1104,VT104,10E/215.
All valves I have are marked VT104 10E/215 and some of them also have a 10P40 marking. None of them have a brand name.
The valves I have look like the attached picture (not one of my valves but I found the picture on WWW)

Corne

[Pedro]

FYI, Langrex in Croydon have them - Ive just ordered another pair - NOS

Rgds
Pete

[IslandPink]

Thanks for the tip-off .
Check them over carefully though , I've seen/had one or duff things from them , although they are always willing to replace .

Mark

[Pedro]

All,

just for info on the ATH33 from AskJanFirst.

Jan has advised me that the ATH33 is not same spec as the ATH38-41 transfomers, as it was designed for a guitar amp using 211's ( ! )

He can do a 10K ATH40 equivalent with extra taps though.

Rgds
Pete