My "new" Bandmaster Reverb.

[Michael Smith]

I purchased this 1969 amp on Reverb, and it arrived in good shape. It is the AA768 circuit revision, as evidenced by the rectangular 150ohm 7Watt resistors on the power tube cathodes to ground. It does have the 125P5D power transformer (just like my 1969 Super Reverb), not the 125P7D transformer indicated on the schematic. Mine came with a 5U4GB rectifier tube, but I put in a GZ34. I noticed the voltages are slightly higher with the GZ34, as measured on the positive ends of the doghouse caps. All transformers date to 1969, as do the filter caps. I will be replacing all of the electrolytics, but first have to get a new multi-meter, as mine is not reading resistance accurately, and I'll want to order replacement resistors for any out of spec ones at the same time I order a cap set.

I had to lower the front "baffle" by a 1/16 of an inch, as the front control panel was binding on the top of the baffle. As a result, there were a few "dents" on the control panel, which I removed and using some C-clamps and a block of metal. When I had the control panel off, on the back of it, there was a number and an emblem I had not seen before, probably the company that made the control panels for Fender. (see photo below) Or perhaps it's an aftermarket replacement, although I doubt it, as there is some light corrosion on it.

The only work I can see that has been done on it is the installation of a grounded power cord, removal of the death cap, and installation of a Sprague 100uF, 100 Volt bias cap. I haven't played it too much, as I don't trust those filter caps, but both channels work, including tremolo and reverb, and there is not much self noise.

[phantomman]

Clean and virtually unmolested, nice!

That's the original front panel plate.

[Michael Smith]

Thanks Phantomman. From what I understand, the BMR is the exact same amp as the Pro Reverb, without the combo speaker cabinet. The company I usually buy capacitor replacement kits from didn't list the BMR, but did have the Pro Reverb kit, and the cap values appeared correct. The schematics called for 525 Volt filter caps, but mine has 500 Volt caps. When I measured the values with the standby switch "off", some of the values were slightly above 500 Volts, but dropped once the standby switch was turned on. I only see 500 Volt caps available, so they should be OK.

Edit: And I don't ever put my amps into standby, except for 2 of mine with diode rectification.

[phantomman]

Another difference between your BMR and a Pro Reverb is the presence of a middle tone control in your vibrato channel (same as a Super Reverb).

[Michael Smith]

Another difference between your BMR and a Pro Reverb is the presence of a middle tone control in your vibrato channel (same as a Super Reverb).

You're right!. The AB668 Pro Reverb did not have a middle tone control. However, the AA1069 Pro Reverb did get a middle tone control on the vibrato channel, as well as a different value tone cap in that position, which makes sense.

Fender sure had a hodgepodge of circuit designs/models in that era. I guess that's why many people "blackface" their silverface amps, to get rid of the variations Fender introduced, although I imagine some of them were for good reason.

[phantomman]

The original AA165 circuit yielded the purest of Pro Reverb tones just as the AB763 was 'da bomb' for Super Reverb's.

[Michael Smith]

Here's an update.

[phantomman]

You might inspect the other solder joints and re-flow any that look suspect.

[Michael Smith]

I did end up re-flowing a few more solder joints. Of course, when I replace the cathode bypass caps, I will be removing and adding solder. I don't have one of those fancy lighted magnifying glass devices that is on a movable arm. I just use an old school magnifying glass and an overhead halogen lamp which I can move around. I may look for a different tip for my Weller soldering station. I noticed most of the YT amp repair guys use the pointed tips. Mine came with one shaped like a flat screwdriver tip. It delivers more heat to the area you are working on, but is less precise.

[phantomman]

I don't have one of those fancy lighted magnifying glass devices that is on a movable arm. I just use an old school magnifying glass and an overhead halogen lamp which I can move around.

Why don't you grab yourself an Opti-visor? These magnifiers are indispensable for working up-close on critical details. Much less awkward than articulated magnifying lamps. You'll discover dozens of uses for them and they're not very expensive.

[Michael Smith]

Why don't you grab yourself an Opti-visor? These magnifiers are indispensable for working up-close on critical details. Much less awkward than articulated magnifying lamps. You'll discover dozens of uses for them and they're not very expensive.

Thats a GREAT idea! I'm looking at them now. I see that some have built in LED lights and different power lenses you can swap in or out.

[phantomman]

If you have decent lighting in your workspace you really won't need the built-in LED type. And they are heavier than the non-lighted versions which often makes them more fatiguing to wear for extended stints at your bench. They are great for certain applications such as under the dashboard or hood of a vehicle though.

[Michael Smith]

If you have decent lighting in your workspace you really won't need the built-in LED type. And they are heavier than the non-lighted versions which often makes them more fatiguing to wear for extended stints at your bench. They are great for certain applications such as under the dashboard or hood of a vehicle though.

I was thinking the same thing about the weight of the batteries. I have good lighting and can add some spot lighting as necessary.

A friend of mine who works on a lot more amps than I do suggested I change out all of the "brown turd" coupling caps when I replace the electrolytics, but I'm inclined to leave them if they aren't leaking DC voltage. Any thoughts?

[phantomman]

Absent an issue, I would leave them in situ.

[Michael Smith]

Absent an issue, I would leave them in situ.

Ya, I think I'll leave them in. They only are leaking a few millivolts of DC

[phantomman]

Keep an eye on them......they may be getting ripe for replacement.

[Michael Smith]

From what I understand, DC leakage will show itself by scratchiness on the pots. If it is extreme, it will through off the bias on the preamp tubes, since the grids will have too much positive voltage.

[Michael Smith]

25K Linear bias trim pot and 10K resistor added to the output tube matching pot on the Bandmaster Reverb. It didn't look so tiny on Antique Electronics Supply's website, lol. All electrolytics replaced, including the cathode bypass caps. This is the first doghouse I've seen where the jumpers were on top of the eyelet board, so I left it that way.



Edit: I wrote the wrong month on the replaced caps, but that shouldn't matter too much in 20 years or so. I was only off by a few days, lol. And yes, I did put a piece of tape on the chassis, indicating the polarity of the caps and the resistor values. I'm not a professional amp tech, lol.

[phantomman]

Did it pass the "smoke test"?

[Michael Smith]

Did it pass the "smoke test"?

Yes it did. I was tempted to take it over to a friend's place with a variac, but was confident in my work. I let it run for about a 1/2 hour and the plate voltage only differed by a volt or 2. I will continue to test tomorrow. It sounded great with a Strat.

[phantomman]

I'd say your new BMR is ready for duty.

[Michael Smith]

I think I will put it back in it's cabinet today and pair it up with my 4 x 10 cabinet. I've been using a 2 x 10 cabinet for testing. I bought a couple of spring type tube retainers and silicone damper rings so I could use a couple of coin base 5881 tubes I have. The bear trap type tube retainers don't work well with those tubes.

The GZ34 is a used old stock Amperex that I picked up for $12 at my local electronic parts store. Most of their NOS tubes are quite pricy, but this one was in a box of tubes they just got in.

[phantomman]

That was a good price for that Amperex GZ34. They generally last forever.

"Jock straps" are near-mandatory for inverted coin-base tubes -- a wise decision.

[Michael Smith]

That was a good price for that Amperex GZ34. They generally last forever.

"Jock straps" are near-mandatory for inverted coin-base tubes -- a wise decision.

From what I understand, the bear trap tube retainers can actually weaken the glass in coin base tubes and cause them to break.

I put all of the components I removed from the amp into a plastic bag and will put them inside the cabinet, in case some "collector" ever wants to reinstall some worn out parts, lol. The power supply and bias resistors all did measure within tolerance, but I though it was a good idea to replace the carbon comp resistors with metal oxide. And the replacement bias diode was only 25 cents, so that was an easy decision. The bias capacitor had already been changed to a Sprague 100uF 100V, so I left that alone. As you can see from the date codes on the power supply capacitors, they all date from 1969.

[Bill Moore]

I wonder if the "modern" components we use nowadays will last that long?

[phantomman]

Tubes certainly won't. I think modern metal-oxide resistors should be good for fifteen or twenty years while F&T electrolytics should deliver a decade's worth of service. My opinion only but based on empirical evidence.

[Michael Smith]

I just noticed that one of the cathode bypass caps I removed was a 5uF, 25Volt. Looking at the schematic, it was the one for V5, the Vibrato 12ax7. All of the capacitor kits sold by Antique Electronics Supply for amps with vibrato come with all 25uF bypass caps, so I guess it doesn't make a difference. I haven't tested the vibrato out yet, as I didn't have the footswitch connected when I was testing on my bench yesterday. I guess that will be my next mission.

Edit: the tremolo seems to work just fine with the 25uF cap.

[phantomman]

You might check for the notorious "trem tick" when next you test the amp.

[Michael Smith]

You might check for the notorious "trem tick" when next you test the amp.

The BMR doesn't have the trem tick. My Deluxe Reverb has it to a small degree, but not enough for me to fix it, until the next time I have to open it up for something.

[phantomman]

Perhaps it had the factory fix applied via Fender's field service bulletin via a previous owner.

[Michael Smith]

The only changes I saw that were made to the circuit was a new bias cap and the changing of the bias resistor (on the output tubes matching pot) from 15k to 10k ohms. But I didn't specifically look for the trem tick capacitor fix. Now I have it all back inside the cabinet. I'll make a note on my schematic to check for that the next time I have it out of the cabinet.

Edit: I looked at the photos I took of the inside of the amp, and did not see a capacitor bypassing the 10M ohm resistor in the tremolo circuit. But after watching a few YT videos on the subject, apparently there are different methods used to fix the problem. My amp DOES have a capacitor (circled in red) installed between the 10M ohm resistor (circled in yellow) and ground.

[phantomman]

I believe that is the fix as specified by the TSB.

[Michael Smith]

I believe that is the fix as specified by the TSB.

I watched the YT video by Brad the Guitologist, and he placed the cap across the 10M ohm resistor, but he did say that the instructions were somewhat confusing. I looked at photos of my Super Reverb and Deluxe Reverb, and neither of them has a cap in either location, so I guess they could be candidates for repair. Although I only remember the Deluxe Reverb ticking. There's a lot you can learn about these old amps. A very experienced amp tech is now sharing space with a friend of mine, so I may make a visit to their shop and get their opinion. At a minimum it will be an opportunity to talk about amps.

Edit: After a little more research on forums (ya, I know there could be a lot of inaccurate information), the capacitor across the 10M ohm resistor was the "old" fix and the cap between the resistor and ground is the "new" fix. So the cap across the resistor (if present) should be removed.

[phantomman]

Just keep in mind amp-tech axiom #1......if it ain't broke, don't "fix" it.

[Michael Smith]

Just keep in mind amp-tech axiom #1......if it ain't broke, don't "fix" it.

Or to steal a quote from guitar repairman Ted Woodford:

[phantomman]

Ayup......samey samey.

[Michael Smith]

When I ordered my capacitors and other parts, I added a white jewel lamp, and also a LED "cool white" #47 bulb. I think it gives it a distinctive look. Hopefully the LED bulb will last forever, although I've not burned out too many incandescent bulbs in amps over the years. The LED bulbs come in a variety of colors, but I don't know how well a non-white bulb would go with traditional jewel lamps.

[phantomman]

Have you decided on a cab and speaker configuration yet?

[Michael Smith]

Have you decided on a cab and speaker configuration yet?

Yes, I will use the 4 x 10 cabinet I built last year loaded with Weber Alnico speakers. I can also use my 2 x 10 cabinet or the 2 x 12 Super Twin Reverb cabinet, or even try my 2 x 15 Peavy Cab. All of the above are 4 ohm. I may even try two 1 x 12 cabinets spread apart in the room. I have one with a Celestion Vintage 30 and another with an Eminence GT-12. It might be interesting to use 2 different speakers. (both are 8 ohm, so I would use both speaker jacks on the back of the amp, which I understand are wired in parallel.

[phantomman]

Any of those should get the job done.