Maine Amplifier Reverb Tray

[MikeHop]

Hi, just bought a Maine (British) combo on ebay, had one back in the 70's/80's just after they stopped making them and loved the sound (really good for a transistor (not IC) amp), and description said crackly pots and reverb doesn't work. Sorted the pots and took the back off the amp expecting to re-solder a wire that usually breaks during years of use, but the reverb tray was missing.....checked out out reverb trays and there's several different input/output impedances, fixing positions, ie. horizontal, vertical end on end...... I'm trying to find someone who has any model of Maine amp in the hope they can tell me the reference number on the reverb tray - they were the same in all models. I then will be able to get a replacement. Can anyone help please.
Mike

[Enzo]

All the pans have about the same output impedance, so the return circuit will be happy. You need to determine the type of drive circuit that feeds it. ANy chanbce you have a schematic for this unit?

[MikeHop]

The output impedances available from Accutronics are: 500ohm, 2250ohm and 10000ohm. I have circuit diagrams of the amp, but I'm no good at working out transistor impedances in circuit. Here's the circuit....
I've tried to attach schematic.

[Enzo]

Accutronics offers those three impedances in their catalog, and an OEM could have them made. But have you ever seen one other than the 2250 ohm? I have not in the last 40 years of this. All the pans you see in the marketplace will be that middle impedance.

Cool. Your drive is the far right circuit. Kinda neat, a whole litle power amp just for reverb. That 150 ohm in series with the drive coil is confusing me. It will be a matter of getting enough drive signal to the pan, current won;t be much of an issue.

Most of the pans we see are either 4AB2C1B or 4EB2C1B. That is for a two-spring. There are also small and large three spring types with 9 or 8 as the first digit. The AB and EB part is the key. The first letter is the drive impedance. Can you find a 4EBxxx pan to try? Borrow one? If it works well, then OK, if not, then try an AB. Fender tube amps almost always use the AB type. SOlid state amps like Peaveys are more likely to have an EB.

The FB pans have even higher drive impedance, but if you stick an EB in place of an FB, it will still work.

In the absence of complete documentation or certain identity of the part, that is how I would approach it.

[MikeHop]

Thanks for reply, appreciate it. I haven't dealt very much with reverb trays apart from replacing one in my Selmer T&B 50. The very fine connecting wires, usually coiled, going to the little transformers tended to break off.
Anyway, I've got a funny feeling that the Maine reverbs could have been 3 spring because they were renowned for their quality, but there again, that driver design could have contributed to that!!! They were fitted vertically (side up) so the 7th digit should be either C (vertical connectors up) or D (vertical connectors down). This diagram indicating an 8 ohm input, seems very similar to the Maine driver.......apart from the 150 ohm resistor. What do you reckon?

[MikeHop]

Just found a photograph of the reverb tank in the same amp as mine. The model No. is 9AB2B1C. Six springs and medium decay time. No wonder they sound so good. Thanks for replies...we almost got there.....
Mike

[J M Fahey]

Just commenting, because you seem to be almost there, but that is a great reverb driver circuit, uses the full rail to rail voltage available to the power amp, wow!!
Which means it needs a high impedance tank or it will put it into orbit
That plus the 150 ohms in series strongly hints at a 2250 ohms impedance (or even higher) input transducer.

[MikeHop]

The 9AB2B1C reverb tray in the photograph, which I believe to be the original tray fitted from new, has an input impedance of 10 ohms and output impedance of 2575 ohms according to the Accutronics spec sheet. As a matter of interest, I can't seem to get one in the UK. I've emailed Accutronics but as it's Christmas I probably won't get a reply for another week or so.

[J M Fahey]

The one in the picture may be anything, I'm not so sure it's the original one in your amp anyway, or to be more precise, it does not match very well that driver circuit.
What size is that 150 ohm resistor?

[MikeHop]

The reverb tray in the picture is the original one and is working perfectly. I've just spoken to the owner. I've bought an amp where the reverb tray is missing and I'm trying to get a replacement. The resistor is 1 Watt with ceramic beads on the legs.

[J M Fahey]

Mmmmhhhh, that driver amp, with the +/- 39V rails shown, can easily supply 20V RMS *clean*, even more if dirty.
That resistor would at least dissipate 2.7W , so a sensible size would be a 5W one.
Too much data against that being an 8 ohms input tank, but hey, it's your amp, do as you wish.

As of the similar schematic suggested by Accutronics, it has no voltages or parts values, it's just an idea of what architecture could be used.
FWIW, similar SS amps used to drive low impedance tanks, were usually fed from a single 12 to 16V rail.
Check old Japanese guitar amps schematics. (Teisco/Univox/Roland/Yamaha/Etc.)

[MikeHop]

Thanks for advice. I'm not familiar with transistor design so I accept your advice. What I will do, though, to try and get a more accurate reverb serial No, is keep checking on Ebay and if one comes up, I'll ask the owner to take the back off and let me know the serial No.
Thanks again, Mike

[MikeHop]

Just had a notification that "kodark has just replied to a thread you have subscribed to entitled - Maine Amplifier Reverb Tray - in the Maintenance, Troubleshooting & Repair forum of Music Electronics Forum." I can't find his reply. I still have Maine circuits.
Mike