Anyone know the right tubes for this? Wabash Deluxe / Danelectro

[wizard333]

The only references I could find for this amp were to a different version that had 2 12AX7s in the upper control portion. This amp does not have those, so before someone links that stuff, that ain't it. This came to me with the wrong tubes installed in at least some slots, but I can't find any reference to what is correct. I'd rather not reverse engineer the entire amp so I'm hoping someone has the answer. This amp is from the early 50s and uses a field coil speaker. Here's what I do know:

V7: 5Y3. All tests were done with this installed, no other tubes.

V6: Standard Octal power tube by the pin out. The other version used a 6L6, this showed up with a 6V6 in this slot and the one next to it (wrong for sure on V5). 6V6 might be correct, or 6L6. Pin 1 is used as a connector tab.

V5: This had a 6V6 in it, which would have grounded the B+. By the pin out, it should have been a 6SJ7. This one I'm pretty sure about (gnd heater gnd grid gnd G2 heater plate).

V4: Standard Octal power tube pin out, but pin 7/8/1 are grounded together. Showed up with a 6Y6 in this slot, which is fine for the pin out, but correct?

V3: Same as above. Showed up with a 12SJ7 here, definitely not correct.

V2: Std. 9 pin 12AX7 type with common cathode EXCEPT: No connection at pin 9 so the heater is not center tapped, heater is connected to pin 5, there is a -90VDC on pin 4.

V1: same as above except no bias voltage on pin 4. This looks like it was set up as a cathode follower to drive some of the controls.

12AX7 type wouldn't work AFAIK in V1/2 due to the 6v heaters no center tap/no parallel.

Thoughts?

[wizard333]

No one? Ok lets try this: Anyone know of a 6v heater dual triode with the same pin out as a 12A series?

[Jazz P Bass]

The heaters are center tapped so you can certainly use 6 volts.

[wizard333]

Where? Pin 9 and pin 4 are not connected to the heater supply.

[Enzo]

V2: Std. 9 pin 12AX7 type with common cathode EXCEPT: No connection at pin 9 so the heater is not center tapped, heater is connected to pin 5, there is a -90VDC on pin 4.

Well that pretty much tells us it isn't a 12AX7 or anything wired like one, unless I misread. Heaters require two pins wired, so if pin 5 gets 6v, which other pin does? Common cathode? I must not understand, 12AX7 has separate cathodes. COmmon cathodes would be like a 6SC7 which is an octal. I also do not understand -90v. Where does that even come from?

Do you have the RCA tube manual or something like it? Th 12AX7 has a 9A base wiring. You can look in the back of the book at all the tubes with a 9A base.
12AE7, 12AT7, 12AU7, 12AV7, 12AX7, 12AY7, 12AZ7, 12BH7, 12DW7, others...

6EU7 is pretty much a 12AX7 with a different pinout, 9LS base. Only one with that base. Heaters go to pins 1 and 2 on that tube. I would see both 6EU7 and 12AX7 in some amps, like Gibson. Why would they do that? Layout maybe. Plenty of old amps out there that started with 6EU7 in some socket that was later rewired to take 12AX7, which is much more common to get.


V6, V4. Wired for power tube. One has pin 7 grounded too. OK, so check the heater string. Is there no CT and no virtual CT? Certainly wouldn;t be the first amp to simply ground one side of the heaters. And some amps grounded one side of the heaters to chasis and ran one wire down the sockets carrying 6vAC, then the other side of each heater was grounded at the sockets. Is that possibly the case here?

If V4 and 6 are power tubes, any chance the tube between them would be a phase splitter for them? Or if V3,4 were power tubes, the other power tube could have driven a reverb maybe?

[wizard333]

By common cathode, I meant they had been soldered together ala the verb driver in a Fender.

The P G1 K of each triode are where they would be on a 12A type, ie. 1-2-3, 6-7-8.

I'm thinking V3/4 are power tubes, they are wired that way with the requisite grid stoppers etc. V6 appears to be an oscillator for the tremolo circuit.

Heaters are interesting. Hard to see what is what given large old caps and 60 ish years of dust and spider webs, and I haven't unsoldered anything yet. Also think my initial readings were confused by 60 year old electrolytics that say "1 year warranty" right on them..........i.e, he's dead Jim.

Here's what I'm seeing on further inspection:

There are two green taps on the PT for the 6.3V heaters. One goes like this: Pin 2 of V6/V5/V4 , Pin 7 of V6/4 are grounded. The other goes to Pin 7 of V5 then to pin 2 of V3, pin 7 of V3 is grounded.
Makes sense for the octals.

It looks to me now like they were doing DC series on the preamp tube heaters. The connections go like this: Red/Yellow bias tap from the PT filtered by a regular biased cap to pin 4 of V2, pin 5 of V2 to pin 5 of V1, Pin 4 of V1 to ground. There is a 15k resistor between the red/yellow bias tap and another reverse bias filter cap that provides the bias at the grids of V3/4. I was probably seeing AC there due to the 60 year old dead caps. Interesting that they were doing DC heaters on the preamp tubes on an amp from the early 50s. Also seems like, if the caps were working, there would be wicked high voltage on the heaters of the preamp tubes, which is probably where that -90v reading came from. To work properly, there would have to be a 12.6 ish volt drop across each heater correct? So should see 25 ish volts DC after filtering.