Picked up a Massie 966 amp head

dobyman

Turntable Addict
I grabbed a Massie Electronics 966 Squire tube amp head and matching 2x12 cabinet today. The 7247/12DW7 tube for the tremolo is missing a pin. Is there another tube I can substitute for it. I have tons of tubes here, but not one 7247, naturally.
Thanks in advance! Oh, here's a pic before I cleaned it. Was sitting unmoved in a basement for 30+ years.
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Tube Depot lists the ECC832 as a suitable replacement.
Nothing in my old tube book except what you already know.
 
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thanks valvenator. I am hoping that is the actual tube that it takes. theres no schematic or markings, but that was the loose tube in the back of the amp when I got it.
 
The 12DW7/7247 is two different tubes in the same bottle: One section is equivalent to a 12AX7,one section is equivalent to a 12AU7.

For many years, when tubes were getting hard to find,I would use a 12AX7 to replace this type. In Ampeg's it always worked fine:)
 
I have a few 12AX7's here. Should I try one? I have 12AU7's too. That's whats in the 3 sockets next to the 6V6's.
 
I guess the 12**7 type tubes are 'swappable' in most situations, just no guarantee they will sound or work right.
A tremolo circuit would be quite sensitive to changes in gain, but it shouldn't hurt to try. I haven't blown up anything yet.;)
Here's a list I made of tubes in the 12AX7 family:

PREAMP & PHASE INVERTER TUBES

GAIN 100: 12AX7 - ECC83, 7025, ECC803, E83CC, 6681, 12AD7
GAIN 100/20: 12DW7 (12AX7 gain 100 & 12AU7 gain 20)
GAIN 70: 5751
GAIN 60: 12AT7 - ECC81, 6201, 6679, 12AZ7
GAIN 45: 12AY7 - 6072
GAIN 41: 12AV7 - 5965
GAIN 19: 12AU7 - ECC82, 5963, 5814, 6189
GAIN 16.5 - 12BH7
 
I guess the 12**7 type tubes are 'swappable' in most situations, just no guarantee they will sound or work right.
A tremolo circuit would be quite sensitive to changes in gain, but it shouldn't hurt to try. I haven't blown up anything yet.;)
Thanks so much. I'll try it and see. If I were to keep it I would try and get a correct tube but I just need to try it out.
I appreciate the info.
 
I ran across this listing: https://reverb.com/item/749031-massie-squire-model-966-1960s-black
The tubes listed were a 6X4, two 6v6's and three 12AX7's. No mention of a 12DW7.
It's a good possibility someone put the wrong tube in yours because that's all they had on hand.
Also no mention of 12AU7's either. In the words of Alice in Wonderland this is getting curiouser and curiouser.
 
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I saw that too, but the odd tube is not in the same place as mine is. Mine is up in front of the transformer.
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I put in a 12AX7 and did a lot of scrubbing. Looks a lot better now. Powered up and it didn't blow up! So far, so good. Will actually plug in a guitar later today, but its dead quiet at idle. New jewel installed. Still waiting on my replacement knob to arrive on Friday.
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Thanks again for all of the info. It is really appreciated!
 
Although this is (officially) a 6V6 amplifier, those transformers look awfully big for that type of machine. Are they original?
 
I wonder if there's a few different versions built on the same chassis.
The one in the listing I posted shows a spot for a reverb jack on the back that is plugged and no reverb controls on the front.
Another post elsewhere mentions 6L6 tubes and reverb, but not tremolo.
 
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I am pretty sure there were a few versions. Some I have seen had the 4 preamp tubes all in a row, where I have 3 and one in front of the transformer. Some have different holes in back plugged or jacked. I think there was a 1268 version also. Similar but different somehow.
I hooked a guitar through it, and it works good. Not super loud, but that could be weak or wrong tubes. Still not sure if it should have all 12AX7's or 12AU7's. My tremolo doesn't seem to work, but I have no footswitch for it, so maybe that's why.
I got it for a really good price, and I know someone will give it a happy home.
 
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I am pretty sure there were a few versions. Some I have seen had the 4 preamp tubes all in a row, where I have 3 and one in front of the transformer. Some have different holes in back plugged or jacked. I think there was a 1268 version also. Similar but different somehow.
I hooked a guitar through it, and it works good. Not super loud, but that could be weak or wrong tubes. Still not sure if it should have all 12AX7's or 12AU7's. My tremolo doesn't seem to work, but I have no footswitch for it, so maybe that's why.
I got it for a really good price, and I know someone will give it a happy home.
If you're not getting enough gain to make it distort try a 12AX7 in the first position. That might help the volume problem. Could also be cheap inefficient drivers in the cabinet.
The tremolo not working might be due to a wrong tube. Like I said, they're usually a sensitive circuit.
As for the foot switch I think generally amps are wired to have effects be on without one plugged in, plus it looks like there's no jack for one.
 
I wonder if there's a few different versions built on the same chassis.
The one in the listing I posted shows a spot for a reverb jack on the back that is plugged and no reverb controls on the front.
Another post elsewhere mentions 6L6 tubes and reverb, but not tremolo.

That's what I'm wondering,because those transformers look a lot bigger than what you'd normally find in a 6V6 amp.Based on how little info there is for these,maybe somebody just thought it was a 6V6 amp,and that's what they installed. The listing you found says 6X4 rectifier,but I don't see one on the chassis. Also,a 2 amp fuse is a little heavy for a 6V6 amp.
By comparison,a Fender Deluxe Reverb (6V6) uses a 1 amp fuse, a Pro Reverb (6L6) uses a 2 amp fuse.

Dobyman,based on the above,I do believe you got yourself a bigger amp than you thought:thumbsup:

A lot of companies did the ''universal chassis'' routine. The old Univox's (real common around here;sound good but damned loud) had more holes than metal in the chassis.
I think they used one pan for every model!
 
If you're not getting enough gain to make it distort try a 12AX7 in the first position. That might help the volume problem. Could also be cheap inefficient drivers in the cabinet.
The tremolo not working might be due to a wrong tube. Like I said, they're usually a sensitive circuit.
As for the foot switch I think generally amps are wired to have effects be on without one plugged in, plus it looks like there's no jack for one.
So should I try a 12AX7 next to the 6v6's or on the opposite end? The speakers don't look like anything high end.
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That's what I'm wondering,because those transformers look a lot bigger than what you'd normally find in a 6V6 amp.Based on how little info there is for these,maybe somebody just thought it was a 6V6 amp,and that's what they installed. The listing you found says 6X4 rectifier,but I don't see one on the chassis. Also,a 2 amp fuse is a little heavy for a 6V6 amp.
By comparison,a Fender Deluxe Reverb (6V6) uses a 1 amp fuse, a Pro Reverb (6L6) uses a 2 amp fuse.

Dobyman,based on the above,I do believe you got yourself a bigger amp than you thought:thumbsup:

A lot of companies did the ''universal chassis'' routine. The old Univox's (real common around here;sound good but damned loud) had more holes than metal in the chassis.
I think they used one pan for every model!
I'll see if I have a 6X4 here. Maybe that goes in front of the transformer instead of the 12AX7. I was just guessing that the tremolo tube went there.
 
I'll see if I have a 6X4 here. Maybe that goes in front of the transformer instead of the 12AX7. I was just guessing that the tremolo tube went there.

Actually,I don't think you have a 6X4. This type has 7 pins,and you cannot exchange it with a 12AX7,as the sockets are different.
 
Ahhhhh thanks. Maybe I'll try all AX7's. I couldn't find any info on one with AU's but that's how I got it. Every one I saw had AX's.
Wish I had a couple 6L6's laying around.
 
A 6X4 is a rectifier tube used to convert AC current to DC. I don't think it could provide enough power for 6L6 tubes.
I usually see them in very low wattage amps and as Arts stated it uses a 7 not 9 pin socket. http://www.r-type.org/pdfs/6x4-1.pdf
I take it the socket next to the transformer is 9 pin.(?) Rectifier tubes are the most basic of tubes and were replaced by solid state rectification which your amp seems to use.

As for the pre-amp tube, it's usually (Note I said usually) the first one, opposite side of the power tubes with the one next to the power tubes being the phase inverter.
The other tubes in between can be a second preamp, reverb or tremolo tube depending on the design.

One question: is the tube next to the output (or power) transformer? I'm guessing output, which might make that the phase inverter. The other tubes might be preamp for first channel, tremolo, preamp for second channel, though without a schematic or close look at the wiring it's anybody's guess. The tremolo circuit might only work on the first input, left channel. I hope the one marked tremolo is an input and not a footswitch jack.
 
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