This Magnavox-branded twin triode was pulled from a 1960's console. The power amp is an 8601-10, but this was pulled from the tuner/phono section. I can't find anything etched on it. The silkscreening says "MAGNAVOX", "Made In U.S.A.", and some numbers and letters I'm having a hard time reading. I don't really care about brand, but I'd like to know what part it is!
The plate structure is unusually "bulbous", and the plate tabs above the top mica are pretty distinctive. Any guesses as to what it might be?
The plate structure is unusually "bulbous", and the plate tabs above the top mica are pretty distinctive. Any guesses as to what it might be?
That looks exactly like it! Could be a 12AX7 or 6EU7, since they've got the same guts. I'll check the filament continuity to see.
The only reason I didn't think that at first is that I pulled a 6EU7 from that console as well, and it was etched with the part number. They're stored in different boxes now, so I haven't compared them side-by-side.
I also pulled a 12AT7, but that was definitely a different plate structure.
Apparently, the other posters didn't read your post very carefully.
It's definitely not a 6EU7. For one thing, none of them have a plate with a ribbed area that's so narrow or rounded. Also, you said it came from the tuner chassis. While the amp has a 6EU7, the tuner does not.
It's a 6DT8.
Here's the tuner section, as shown in the Sams. No 6EU7s or 12AX7s.
As you can see, it has two 6BA6s, which are 7 pin pentodes, a 6DT8, which is a 9 pin dual triode, a 6BE6, which is a 7 pin heptode, and 6AL5, which is a 7 pin dual diode.
So, if it came from the tuner and it's a 9 pin, it's a 6DT8.
Attachments
Apparently you didn't read his post very carefully either. He said "tuner/phono section"
A 6DT8/12DT8 is basically a 12AT7 with a shield on pin 9. I've never seen a 6DT8/12DT8 or a 12AT7 with innards like that.
Well, that is what he said. Here's the Sams. Please point out the "phono section".
Unless he has a different variant, which is possible, there isn't one. These old console stereos typically had inputs for a ceramic phono cartridge only.
I don't think I've ever looked at a 6DT8 but all the 12AT7s I've seen have very short plate structures.
I'm curious as to what evidence you base this upon. I think the OP is the one who needs to make such a declaration.JonSnell has won the race.
Best regards!
Again, I would refer you to the Sams which I posted. I concede that it's possible that the console he has is a variant of what's shown, especially since he said he pulled a 12AT7 from it and there's no 12AT7 listed in the Sams. Or it's possible that he listed the wrong chassis number entirely, I suppose. Or that an incorrect tube was put in somewhere at some point.
But the Sams indicates that there is only one 6EU7, which is in the amp section. He already found one and it's clearly marked.
The Sams shows only four 9 pin tubes. The 6EU7 and a pair of 6BQ5s in the amp and a 6DT8 in the tuner.
If he has a meter he can tell the difference easily if both heaters are intact. The 6EU7 will show continuity between the heater pins, which are 1 & 2. The 6DT8's heaters are pins 4 & 5.
A 12AT7 or 12AX7 will also show continuity between pins 4 & 5, but they will also show continuity between those pins and pin 9, which is the heater center tap. The 6DT8 has no connection on pin 9, so no continuity between 4 & 5 and 9 would rule out any of the 12**7 types.
If he does have a different version that uses a 12AT7, I suspect it's not part of a phono preamp section. As I pointed out, very few console amps had magnetic phono inputs and I've never noticed one in a Magnavox. And a 12AT7 is not a tube that is typically used in phono preamps anyway, I assume since it has lower gain. Typically you see 12AX7s used in phono preamp sections in vintage gear.
Last edited:
Sorry it took so long to follow up on this, been a very busy couple days!
Okay. So.
It's not a 6DT8, because I have the one that I pulled, and it's labeled, so it's not this one. I think this power amp was used with multiple console variants - this one had a turntable and a tuner.
It's not a 6EU7, because there's continuity between 4-5-9. The plate structure is also markedly different from the 6EU7 that came from the power amp. BUT: I've seen other pictures of Magnavox-branded 6EU7s that *do* have this plate structure (see pic below - NOT MINE, this is from an eBay listing).
So I'm really tempted to say that it's a 12AX7.
Side note - I don't really understand the practice of using both 6EU7 and 12AX7 in the same piece of equipment. I've seen it several times. Wouldn't it make more sense to standardize on one or the other?
Okay. So.
It's not a 6DT8, because I have the one that I pulled, and it's labeled, so it's not this one. I think this power amp was used with multiple console variants - this one had a turntable and a tuner.
It's not a 6EU7, because there's continuity between 4-5-9. The plate structure is also markedly different from the 6EU7 that came from the power amp. BUT: I've seen other pictures of Magnavox-branded 6EU7s that *do* have this plate structure (see pic below - NOT MINE, this is from an eBay listing).
So I'm really tempted to say that it's a 12AX7.
Side note - I don't really understand the practice of using both 6EU7 and 12AX7 in the same piece of equipment. I've seen it several times. Wouldn't it make more sense to standardize on one or the other?
Interesting. It sounds like it is something from the 12**7 family given the continuity between those pins. Please post a pic of the tuner / phono section that it came out of? The same section may be shown in a Sams for one of the other Magnavox models.
This is from a console that used the little SE 6BQ5 amp shown in the Sams I posted, right?
I've heard that the 6EU7 has a spiral heater which is supposedly similar to a 7025. Not sure why they would use both it and a 12AX7 in the same unit either. They did use 6EU7s a lot. Could it be that the bean counters figured there would be less labor cost if only two heater pins were involved??
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.