Solid state valve replacements

[regentone001]

I seem to remember that there were solid state replacements for the valves used in the CDA panel of the PYE 697 chassis. Were there other types of solid state replacements and were they any more or less reliable than the thermionic valve?
Steve

[sortedradio]

There are solid state replacements for the 5U4, 5AR4 and 5Y3 type rectifier valves which I believe are more reliable. However they can make a difference to the sound depending on the application.

Martin

[ukcol]

Originally Posted by regentone001

....used in the CDA panel of the PYE 697 chassis

When the PL802 luminance output valve was in short supply a solid state replacement was made available called the PL802T. IIRC it was not as good as the valve as it provided less output (hence contrast).

[turretslug]

There have been solid-state work-arounds for series regulator valves, alleviating the emission-limited life and blazing heater-power needs of these hard-worked valves, e.g. the 6080 and friends, but I suspect many were equipment-tailored and depot-fitted in small quantities. "Universal" just-plug-in semiconductor options have always been tricky to concoct for all the eventualities of a thermionic predecessor- as the Fetron folk no doubt found. I wonder if the likes of the '60s/'70s US military ever issued a requirement for a "6080T"?

[bikerhifinut]

I seem to remember some SS plug in replacements for ECC series small signal valves, in particular ECC83/12AX7, this was on a US guitar amp site. I wonder how they made em? they looked a lot shorter than the valves. I assume they will have been high voltage FET based devices?
http://amtelectronicsusa.com/productpage12AX7WS.html
A

[Boater Sam]

EM34SS

https://www.vintage-radio.net/forum/...ad.php?t=97804

[G6Tanuki]

In the 60s and 70s International Rectifier corp. offered a range of semiconductor arrays for valve-rectifier replacement: I made extensive use of their "IR14" which looked just like a bakelite Octal valve-base with epoxy resin filling the hole where the valve would normally have gone.

Also in the 1960s there were plug-in valve-rectifier replacements that took the form of a bakelite octal base to which a tubular aluminium can about 5 inches high was fitted. There was a threaded brass rod that fitted down the centre of the can and into the octal-base spigot: on this rod there were discs of Paxolin between which a number of BY100-type silicon diodes lived.
This type took the place of valves in things like the Pye F27AM/F27FM base-stations, where they delivered 500-600V of HT at plenty of milliamps to power nice beefy output valves like the QQV06/40A

[Argus25]

Yes, the basic idea was to replace valves with semiconductors. The idea was pioneered by Teledyne in the 1970's. High voltage J-Fets have very similar electrical properties to triodes, in that they run with a negative input voltage and are transconductance devices, meaning they convert a varying input voltage to a varying output current.

Electrical equivalents were made for triodes like the 12AX7 (later to be cloned by Amtel as noted in post #6). The real trick was to make a solid state substitute for a pentode.

Teledyne achieved this with the TS6Ak5, which contains two J-fets in a modified version of the Cascode configuration. This provides input to output isolation, such as afforded by the screen grid in a pentode.

Here is a link to a radio which uses these Fetrons:

http://worldphaco.com/uploads/WORLDFETRON.pdf

However, as much as Teledyne tried, there was a big problem. In a real valve if you take the input grid positive with respect to the cathode, the conduction is "soft" in onset. With a J-fet its sudden. So for many valve circuits that rely on grid to cathode rectification (for example self bias in an oscillator in a radio) the Fetron would malfunction when plugged in place of a valve and produce multiple output harmonics. Yet in most other applications the Fetron would work as a plug in substitute for a valve just fine. Many (double triode equivalents) made by Teledyne were used in the front end of Mesa-Boogie guitar amplifiers.

The Fetron has lower noise, a higher amplification factor, no microphony, and no heater power consumption compared to a valve, so yes, for the most part they are in fact superior to a valve, unless they are hit by an EMP, then you might be out of luck.

[G6Tanuki]

I also remember some obviously commercially-made replacements for the EB91 double-diode: what amounted to a bakelite B7G valvebase-plug with what I guess must have been a couple of Germanium diodes (AA119/OA85?) soldered-and-epoxied over. They had a 4BA nut recessed into the top-face, so you could screw in a suitable rod to the pseudo-EB91 to gelp with insertion and withdrawal: being so squat if the valveholder was a 'skirted' type you wouldn't have been able to get a pseudo-91 out without this rod to help!

Saw these in a number of bits of instrumentation gear.

[TonyDuell]

I seem to remember that Heathkit sold ready-built replacements for the valves in their valve voltmeter kits. I think they were EB91 and ECC8x (I can't remember which double triode was used).

Whether these were universal replacements, or just worked in that kit I do not know.

[HamishBoxer]

I think I still have a solid state PL802 NOS hiding in my archives.Certainly used them in the Pye 205.

[MrBungle]

Originally Posted by TonyDuell

I seem to remember that Heathkit sold ready-built replacements for the valves in their valve voltmeter kits. I think they were EB91 and ECC8x (I can't remember which double triode was used).

Whether these were universal replacements, or just worked in that kit I do not know.

I nearly vought a FETRON equipped Heathkit VTVM a while ago on ebay. Something in me didn't fancy the hassle though so I skipped it. Having some regrets now