F5 power amplifier

The input FETs are not safe above 30V or so. You will need a cascode.

It will work fine if you use the cviller F5c boards and use just one output pair. Keep dissipation within the 30W target per device and you will be fine.

400VA sounds about right as a universal power supply.

Ok, I read about it in the art_f5_turbo.pdf, so basically I could go plain F5 at risk, or try a variant with cascode like the input part of V3 and maybe a higher gain while lowering the bias. That would give me more power, but it will leave Class A earlier, if I understood it correctly. Point is I don't want a monster heatsink that would be required in order to go up in Class A power, so I would sacrifice that for more power in the cases when it's needed.

Regards, Stefan
 
Really, Well just who was using those JFETs in the Japanese market?

The answer would be shorter had you asked who wasn't.

The Japanese industry is highly interlinked, both through tradition and long term contracts (which often also have historic links).
On top of that there are huge conglomerates in Japan.
Take e.g. the Mitsubishi corp., everything from banking & insurance, to consumer electronics and parts, to cars and building oil tankers(MHI).

Suppose Toshiba transistors developes a part for Toshiba consumer electronics.
After an average manufacture span of 20 years, Toshiba transistors will develop a successor part, and the old one goes obsolete.
If Toshiba consumer electronics has no need for a successor part, the old one goes obsolete and no replacement.
Even if production of the old part may still be profitable for the foreign market, Toshiba will halt manufacture.

A US company also primarily developes a product for the local market, say Motorola.
It will also start selling abroad once the local market has reached maturity.
The American company will continue manufacturing till total volume of both domestic and foreign demand has dropped to a level that's not worth the effort.

In Japan, the communication path between JFET manufacturer and JFET end user is short, and highly interactive, within a conglomerate as well as between e.g. Toshiba and Sony.
They make both The part for A market, and vice versa, but not just A part for A market.

The JFET numbers have been available in the west for quite a long time.
I can give you plenty examples of Japanese devices that were barely available abroad, with room for growth, when manufacture was terminated.
 
The one and only
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There is too much concern about these particular Jfets for the front end
of the amplifier. Yes, the 2SJ74 and 2SK170 are really superb, particularly
on the noise front, but this is not as important when we are already dealing
with line level volts instead of millivolts.

You can still get the Fairchild J174, J175, P1086 P channel devices from such
places as Digikey and Mouser, and they are cheap.

The N channel are even easier to get, such as the Fairchild J111. Worst
case you might have to parallel two, but even that is unlikely. You might
have to select them, but at prices like $0.11 for quantities, you can hardly complain.

Better buy them before I do....

:cool:
 

6L6

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You can still get the Fairchild J174, J175, P1086 P channel devices from such places as Digikey and Mouser, and they are cheap.

The N channel are even easier to get, such as the Fairchild J111. You might
have to select them,
but at prices like $0.11 for quantities, you can hardly complain.

If selecting, we should be aiming for an Idss of 8-10 or so?
 
These others are inexpensive enough that you can match P and N for Idss or gm --

I had some boards burned to allow use of the surface mount devices, or the 2N5460/2N5457 etc. which have a different pinout. You can buy 25 of the SMT like the MMBF5460/1/2 for the cost of a six pack of Bud.

Cordell shows a dual N-Channel input stage in his book, but its just not elegantly simple like the F5.
 

6L6

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Mr Pass, I'm wondering if Linear Systems ever gave you a reason their parts have been delayed so long?

I know the answer to that, the J74, being a P-channel Jfet, is significantly harder to make than a N-channel (and more expensive), and they have been having trouble getting them to good quality.

My understanding is that they should be available soon.