Huge triode

[David Simpson]

A pal has just acquired a huge 12" tall Triode with a 3 3/4" dia. base, which he'll be fetching over for me to hopefully test. No ident printed on the glass or the base. I asked him to get a magnifying glass & look inside at the glass pinch.
He can see "8615 or is that 861S" etched at the top, with "E followed by a curly C" below. GEC maybe?
Several years ago, I tested an STC4212D making a bespoke 4 pin valve holder, and hopefully that will fit or can be adapted. He's metered continuity across two of the pins, so that bodes well.
Any info &/or advice most welcome, please.

Regards, David

[murphyv310]

Hi.
I had one and it went for a large sum of money.
Some Audio guy jumped at it.

[jjl]

It could be a GEC V1505 - GEC's "An Approach to Audio Frequency Amplifier Design" book featured a 300W push-pull amplifier using this type.

John

[Hartley118]

That certainly looks like an STC 4212 as used in the Bryan Savage 1kW audio amplifiers designed for vibration testing, but also favoured by the likes of Rediffusion for their programme distribution. ISTR the output pair were transformer driven from a pair of KT66s.

We used to use them for powering automated audio mixing desks with 117V 60Hz. Back in the day, that's what the floppy disk drives needed when ordered for the US market.

I have a 'left over' 4212 in the loft somewhere, but, splendid thing though it is, I've never found a use for it.

Martin

[Vintage_RC]

I have a 4212 on display in my valve collection and it is certainly impressive. Mind you it looks small compared with the MT9L that Wendy Mott kindly donated to me.

[Vintage_RC]

A photo of the 4212 and the MT9L

[joebog1]

It looks the perfect match to amplifying a crystal set. Might need a bit more drive though .

Joe

[David Simpson]

Like Trevor, I flogged the 4212D for a wad of dosh. But then, I have STC's 1940's Valve Data Manual for their range of big thumpers, which contains families of Gm graphs for each valve. Hence, was able to test it with my DC tester (admittingly at the lowest of the Va's), to compare with STC's spec. Thus, providing a graph of STC's & my own tester's Gm to the purchaser. In fact, those who know me, ken that I always provide tabulated graphs for big power valves, when I've flogged them in the past. KT's, PX25's, etc. But that's only once in a blue moon, as I'm not a wheeler dealer.
Thanks, guys, for revealing the probability of this beast being a V1505. I'll update when my pal brings it over next week.

Regards, David

[Station X]

Thread reopened at OP's request.

[David Simpson]

Thanks Graham. At last I have this valve in my possession. Looks in mint condition. Pity it didn't come with it's original box, as that would have enhanced my belief that its NOS. Will start to re-assemble the thumping big heater rig, and Ia/Vg testing rig.
Will keep folk informed.

Regards, David

[Vintage Engr]

That's very interesting, I also have one of these that I use as a "Techno-ornament".
I was given it by a lecturer, when I was servicing an industrial video projector at BAe, about 30years ago.

I was up a ladder, adjusting the convergence, on a Barco CRT projector, & being as quiet as possible, as there was a lecture in progress. When the students left the hall, the triode was on the lecturer's desk.
I made some comment about "you don't get many of those to the pound", & when seeing my interest, & after a brief discussion about old technology, I was given it.

Like David, I have never found a base for it!

David.

[lesmw0sec]

Originally Posted by Hartley118

That certainly looks like an STC 4212 as used in the Bryan Savage 1kW audio amplifiers designed for vibration testing, but also favoured by the likes of Rediffusion for their programme distribution. ISTR the output pair were transformer driven from a pair of KT66s.

We used to use them for powering automated audio mixing desks with 117V 60Hz. Back in the day, that's what the floppy disk drives needed when ordered for the US market.

I have a 'left over' 4212 in the loft somewhere, but, splendid thing though it is, I've never found a use for it.

Martin

You remind me of the one we had in the standards lab at Winfrith which it was my job to maintain. I recall the red-hot anodes at full o/p and also seem to recall that there was an unbalance detection trip circuit of some sort which was quite easy to engage.

[David Simpson]

Looks like the brown marks on the ceramic underside could be old dried flux. Also a bit on the Anode pin. A VMARS pal has suggested that there is a break within the valve base, and perhaps a previous owner has attempted a re-soldering remedy. We're going to heat up the filament with my 24V DC supply & dropper again - next Sunday. Then apply 2.5KV from my huge HV Megger between the Anode pin & Filament. Might encourage some Ia if the break is almost touching. Following that - a thorough de-soldering of the anode pin followed by a quick re-soldering. One can but try.

Regards, David

[Diabolical Artificer]

Maybe the previous owner just re-soldered the filament pins, dry joints OC filament/heaters is something I've had on a few valves.

Nice valve, Andy.

[David Simpson]

Aye, Andy, thankfully the filament connections were fine. Should've posted these pictures sooner. 'Fraid this big fella has had to vie for attention with the Ekco A22 & exhausting jobbies outside on our wee smallholding. For the last several days the flippin rain has driven me inside. Electronicing & blethering on the Forum.
The spec for the 4212D I had(and the V1505) is Vf = 14V & drew 6A. This beastie already drew 6A at just 9.52V. My hefty 24VDC supply(2 12V Tractor Batteries backed up by a Sailor N1404 40A Marine PSU), along with the 10A rated Dropper, could give more closely to 14V, but hey - that filament might light up like a halogen headlight !
(Googling "STC4212" - bring up one on eBay for over £700!). I got about a quarter of that several years back for the NOS boxed 4212D, & that included an A4 plotted graph of an Ia/Vg curve.

Regards, David

[Diabolical Artificer]

Perhaps try one battery EG 12v - though most automotive batteries are more like 13.5v for first power up. Not sure with these triodes if the filament needs powering for 20 minutes before applying HT, quite a few big valves like MVR's and other transmitting valves specify that after a long time not powered up.

These big old triodes are like phoenix feathers, wonder what they cost new?

Andy.

[emeritus]

At least your large valve is a valve. When I browsed the on-line Marconi collection catalogue shortly after it had gone to Oxford, I came across this alleged "Giant Radio Valve", which I immediately realised was in fact a bi-post base, high power incandescent tungsten lamp bulb which, from its colour temperature marking, was intended for studio colour photography or filming. I emailed the curator, enclosing scans from text books with a line drawing of this type of bulb and a description which mentioned its (1930's) date of introduction, but got no reply, and the website still has the incorrect description today.

[David Simpson]

Took the filament voltage up to 14V & it drew 9A. Had tried resoldering the big Anode pin, but all to no avail, just couldn't achieve even a uA of Ia even with 2KV on the anode. After 15 min, the pinch succumbed to the heat & blew the vacume at the tiny wee nipple. The chap who owned it said to just skip it. As it was only discovered in a gash box of glassware acquired from an auction.
So, Moderators, this thread can be closed. David

[Radio Wrangler]

There might not have been much vacuum to start with if that much heat was getting from the filament to the pinch.

Oh, well, it's an ornament now.

David