Hi GTC, correct, all done. Thank you.

Today's testing was on common 7-pin valves. I used a B15 radio from the to-be-scrapped pile - the radio works, but the cabinet is wrecked.

The radio uses the usual line-up: 6BE6, 6BA6, 6AV6, 6AQ5, 6X4. These are very common valves, so I have approximately 40 of each.

All 6BA6's worked except 2 which lit up but did nothing. The 6AU6 can also be tested in this socket. This valve gives the appearance of being more sensitive, but it distorts on very strong stations. This is because it's an audio valve (sharp cutoff) and ignores the AGC attempts to rein it in. All 70 or so 6AU6's worked. I also have a 6136 valve, this worked too. Lastly, I have a 6AK6, it has the same connections, but it's a 1.1 watt output valve. Would it work as an IF amp? Only one way to find out. In fact it did work, for about 2 seconds, then it started screaming. At least I know now.

There were a few unmarked valves that looked like they might be similar. One worked, one screeched, and one turned out to be a working 6BE6. So the screechy one is still not identified.

Next was to test 6AV6, 6AT6 and 6AQ6. All of them worked. There's a bunch more similar valves in existence but I don't have them.

Then onto the 6X4. These are famous (or infamous) for the heater escaping from the cathode and sticking up to the top of the glass. Even though, they still work. Of my collection, most valves worked. There was one that gave me a bad feeling when I picked it up. Sure enough, one anode was shorted to the heater, so it went straight to the bin. Another made me uneasy, but there were no shorts. But in the radio it sparked inside, followed by a huge amount of smoke from the bias resistor. So in the bin it went too. Even though the bias resistor was now charred, it still measured correctly.

Lastly, it was time to test the collection of 6AQ5, 6HG5 and EL90, which are all identical. In fact many of the newer ones say 6HG5 6AQ5 on the side. Why someone came up with the 6HG5 idea will probably never be known. All but 3 worked. 1 produced no output, 1 worked but the output was very low, not worth keeping and the last had an unusual failure. I plugged it in, and nothing happened, but when I pushed on the valve it suddenly came to life. After removing it though, I couldn't get the next one to plug in. When I looked down, there was a valve pin stuck in the socket. Most fortunately it was pin 7, which is duplicated on pin 1. In an emergency the valve can still be used provided that pin 1 is wired up.

Tomorrow I will check some common 9-pin types.

Today I used once again, the condemned 11-81 that's in the garage. Like the B15, it works, but the case is cactus. The valve lineup is 6AN7, 6N8, 6BD7, 6AQ5, 6V4.

Firstly, the 40+ examples of 6AN7 and 6AN7A all worked.

Next, the 6N8. 38 worked, 2 failed - they both screamed at me. Then I tried out all 10 6AD8 in the same socket, they all worked, although one was very low gain.

Then, the 6BD7 - all 8 worked.

So far, each of these valves comes in a Philips Innoval version, and in a normal Radiotron version.
The Innoval types have silver-plated pins, which need to be polished up every so often with stainless-steel wool. The 6N8 / 6AD8 need special mention - the Innoval type are grey inside, while the later ones have silver mesh. The 6N8 is a bit prone to go low gain, or crackly. Still, they are exceedingly common, so finding a good one shouldn't be a problem. The 6AD8 is practically identical in every way (has lower gain), but seems to be favoured for use in reflex designs.

While I was working on the 6AN7's, I happened to notice that the 6AQ5 has a crack in the glass, at the base, going nearly halfway around. I expected it to suddenly go flash and bang during the session, but it bravely held on and continued to work.

Lastly, the 6V4. There's 2 types of 6V4. The early type is as tall as a 6M5 (or 6GW8), and has 2 separate halfwave rectifiers stacked one above the other, separated by 2 mica sheets. Their downfall is silver migration just inside the base, which eventually shorts all the pins together. I've heard this can be fixed in a very crude way, but I'm not going to try that. This disease has affected almost all my old 6V4's, with measurable resistance between various pins. So sadly, 8 of them had to get binned, even though they otherwise would work.

The much more common short version is much like a 6X4 with larger fins, and doesn't have the above problem. These all worked, except for one that started flashing after it warmed up. It took a while though as I had to examine each valve's cathode under a light to make sure it was intact. A few of the valves were the equivalent EZ80 - these all worked too.

The larger 6CA4 / EZ81 also fits in the socket, and these all worked.

Lastly, my only example of EZ82 - these are meant to have the cathode and heater joined externally (or at least that's how it was in the radio I got it from). It looks exactly like the old 6V4, and also had its disease. Sadly, another one for the bin.

I'd expect that eventually all the remaining old 6V4's will die in the same way.

Some valves had no markings and I'd made educated guesses as to what they might be. The ones marked as 6AN7 and 6N8 were tried, and fortunately all my guesses were correct. These leaves just a handful of unknown valves, and maybe I'll work out what they are one day.

I had another think about the above double-decker 6V4's, and decided I'd keep them. The leakage is in the the mega-ohm range, and the rectifier is the one circuit that is low-impedance - so the leakage will have next to no effect. Therefore I tested all those rejected valves and they all worked, so they're back in the collection.

Now, to today's testing. I used a Philips push-button job that has numerous issues, but at least it works, sort-of, on MW.

The valve line-up I suspect should have been ECH81, EF89, EBC81, EL84, EZ80, DM71, but in fact it had ECH81, 6BX6, 6BD7, 6M5, 6V4 and DM71.

So, first to test my ECH81 collection, which is 4x ECH81, 1x CV2128 and 1x 6AJ8 - they all worked. Next, there's 6 Russian valves which looked like beefy output valves, but once I looked them up, they were listed as directly compatible with ECH81. Well, what can I say? They are not compatible. 5 of them screeched in identical fashion, and 1 worked. So maybe whoever decides these things needs to have another look.

Now, since this radio has a 6BX6, it means I could test all those valves with the same pinouts - in my case, EF89, 6BW7, 6BX6/EF80, 6BY7, 6EH7, and 6EJ7. Most of these are stored in a box that I never dared to enter - it's full of TV valves that will never be used for anything. But now I had to sort out the pile. So, first came at least 150 6BM8's, followed by an avalanche of 1S2, 1X2A, 6AL3, 6BL8, 6ES8, 6U8, 6DX8 and a bunch of other 9-pin types normally used in TV tuners. Lastly, this left I guess about 150-200 IF valves as listed above.

It took quite a few hours to test them all, and about a dozen failed and were thrown out. One of the good ones, a 6EH7, became a permanent replacement for the 6BX6 that had been in the radio.

Then I put the rest back in the box (minus a few that had gone gassy over the intervening years), and put everything away again.

More tomorrow.

Today's episode pretty much completes testing of miniature (7-pin, 9-pin) valves, except for battery types.

I used a Stromberg-Carlson 5A29, a Mullard MAS-1001A, and one of those plastic Philips 5-valve type.

I couldn't find a schematic of the 5A29 anywhere, even radio museum has nothing except a photo. The valve line-up is a bit unusual: 6J8G, EBF35, 6SQ7GT, 6V6GT and 5Y3GT.

The Mullard is a 4-valve type with reflexing: 6AN7, 6N8, 6M5, 6X5GT, and the Philips is the usual for them: 6AN7, 6BH5, 6BD7, 6M5, 6V4.

I tested all my 6SQ7GT - all worked. Then the EBF35 - all worked except one which lit up but did nothing. One of them made loud farting noises because the red paint had fallen off. This was fixed with aluminium foil, a wire, and some black sticky tape. No soldering.

The EBF35 has the same pinout as the EBF2G/GT, and the 6AR7GT. The 2 gold-plated EBF2G's were tested successfully. The 6AR7GT's had already been tested a while ago, but I tried one just to support my hypothesis - it worked.

Next was to test the 6M5 collection - I've never come across a faulty 6M5, and all 37 of my spares worked. A fugitive 6CA4 was found and tested - worked. Lastly were 14x 6BH5 - these all worked too.

All of the 6BH5's, and most of the 6M5's were Innoval types, so they need the pins cleaned every so often.

Out of the 3 radios, the best by far (not surprisingly) was the Philips 5-valve. They may look cheap and nasty, but they really perform. Despite that, the 6BH5 that came with it was a bit on the weak side, so it acquired a better one.

So, just a few octal types left to test - 6B6G, 6B8G, 6G8G and 6U7G, and then this story will be over.

"The EBF35 has the same pinout as the EBF2G/GT, and the 6AR7GT."

Is that so? My usual source of valve data (Franks) fails me on the EBF35, which I had always assumed was a sharp cutoff version of the EBF32 sharing the same pinout.

The 6AR7's pinout throws the rule book out! E.G. heater on pins 1 and 8 instead of the octal standard of 2 and 7.

Only the anode and Diode 2 are on the same pins as the EBF32, which also has the same pinout as the very similar 6G8G

Back in the 70s I wrote a book which grouped all the different kinds of valves together depending on their pin connections. I still use it to find possible equivalents as you've seen in this thread. Sometimes of course even with the same pins they are not really equivalent, but at least they are unlikely to cause damage.

This book has not yet been transferred to the computer, so there isn't a way to give others access to this info. There's lots of pencilled-in corrections and additions to be dealt with too.

It is from this book that I discovered the possible equivalence of the EBF35, the EBF2G and the 6AR7GT.

Well whaddya know?!

EBF35 is close to the 6AR7 (with its odd heater pinout) and may well be interchangeable if pins 7 and 2 are connected together.

I wonder why they did that when the 6G8 pinout seems to not have any disadvantages and using that pinout would have allowed both the 6AR7 and the EBF35 to be a plug-in upgrade as well as a valid replacement.

Today's testing was done with the Tela-Verta radio that's been a pain in the posterior ever since it got here, and it didn't let me down today.

Firstly, tested the 6B6G's - 2 failures, lit up but no output. Still got about 15 working spares.

After testing the last one, found a VR99A in the box, so came here to the computer to find out what it's equivalent to - it's a ECH35 - went back after about 20 minutes, and now the 5Y3 in the Tela-Verta was no longer alight. Pulled it out, and it was severely damaged. The filament no longer exists, and the top section of one of the anodes had been vaporised. I don't know what caused it either. With it out, the voltages and resistances all seemed normal, so I tried another 5Y3GT, and the radio worked. But the valve does get rather warmer than it should, so there must be some issue with that radio. (Yet another issue I should say).

As for the VR99A, it was tested in one of the Pyes still on the bench, didn't light up, the heater was burnt out, so in the bin it went.

Back to the Tela-Verta, now to test the 6U7G's. I wasn't going to clamp a goat shield on each one, so I just dropped a round can over the valve and used an alligator clip to earth it. All of my spare 6U7G's worked, as did the few 6J7G's that I tested. There was a 6K7GT (my only one) but the heater was open, so another one for the bin. I decided to use a 6J7G permanently in the radio and dispense with the clumsy goat shield whose earth wires kept breaking off.

I'd still like to know what caused the 5Y3GT to die in such agony and distress.

Tomorrow the 6B8G/6G8G collection will be tested, along with a bunch of unknowns.

Tested the 6B8G and 6G8G valves - one 6G8G failed (lit up but no output), everything else worked fine.

Found 3 unknown octal valves. In the sunshine I could see that one is a 1K7G, although I think the filament might be blown, but I'll keep it until it can be confirmed. I don't have any of those 2 volt country radios.

The next one looks rather like a 6U7G with its distinctive round metal shield at the top, but it's something else. And the last one is a short metal valve with a top cap. Apart from confirming the heater is intact pins 2 and 7, there's not much else to work with.

So, this little exercise is over.

Bear in mind that the ECH35 and the 6AR7 have the heater on pins 1 and 8, unlike most other octal valves. So your VR99 might be OK.

One should never assume that the pinouts follow the convention like octal, 2 &7 heaters 3 plate and pin one shield. Metal tubes can have shields on pins other than one and subbing a glass tube with metal can be interesting (like 250V on the body in one case) when octal pin one is used as a tag of convenience.

Noticed a 11-7 sitting in the corner, it works although the dial cord is broken. Valves: 6AN7, 6SK7GT, 6SQ7GT, EL33, 6X5GT.

There's a whole bunch of spare 6SK7 and 6SJ7 (both metal and glass ones) so I tested them all, only one failure, o/c heater. The 6SS7 has the same connections, so the one I have was tested and it worked. I noticed that the 6AC7 also has the same connections, it's one of those valves that everyone has but it's useless. Anyway 2 of them worked and all the rest did not. I didn't throw them out though, because I assume the conditions were not correct to operate properly. (It's a sharp cutoff pentode for TVs)

A rogue 6SQ7GT was found, but it also had an o/c heater. A metal 6SR7 was also located, it has the same connections as the 6SQ7, it worked but with an amplification factor of only 16, the volume was less.

Now for the mystery part. I found a 6W6G and a 6Y6GA (these are output valves). When tested, the radio hummed and the 6X5 flashed over. Yet when tested in the Pye, they both worked fine. Both radios use a EL33 as standard. The connections are supposed to be absolutely identical, apart from the EL33's red shield. Weird.