Early 1971 Fender Bandmaster Reverb ??

[Brett Cooper]

I acquired a ‘71 Bandmaster Reverb about 4 years ago. It has a very sweet and “Fendery” tone. But, for some reason, I seldom use it. I typically take my old Bassman 50 when I play guitar. . . . with a 2x10 cabinet that I got from Mojotone.

I’m not the guy that likes to change the “DNA” of an amplifier or instrument. However, I wonder if it makes sense to do something with my Bandmaster Reverb in order to make it a really useful amp for pedal steel. I’m aware that by installing a bigger output transformer I can beef it up.

For someone experiencing with an amp of similarity . . . Is it wise to make big enough changes to make this a gigging steel amp?

[Paul Sutherland]

Don't do it. You'll devalue a very desirable vintage amp. Just accept it for what it is, and use something else for when you have to play loud.

That amp will only get more valuable as time goes by if it's left stock.

[Bill Hatcher]

not worth the trouble. just buy a twin reverb and you will have the amp everyone used for many years.

the bmr amp....guys used to take those and gut the head and put it in a single 15 cab and make a poor mans vibroverb out of them for rock/srv sounds.

they dont have the headroom for clean steel sounds, but grind out just fine for rock/blues stuff

[Jim Sliff]

If the BMR is generally loud enough, or just a bit lacking in punch, it may be just fine in theory. DON't change the output transformer.

The weakness for pedal steel is in the speakers. They are neither efficient enough nor do they have the kind of headroom when hit with a wide frequency range as is common with pedal steel. The original speakers can be removed and saved in case you re-sell the amp. The Weber California series are excellent replacements much better suited for pedal steel.

But if it has not had normal service is 15 years or more it needs it - and that can weaken the sound. It can also damage the amp if a power supply capacitor fails, which can happen with absolutely no warning. The following also applies to your Bassman 50:

power supply and bias electrolytic capacitors have a service life of appx 15 years - less if the amp sits for extended periods (a couple of years without powering up is generally too long).

There's no way to visually confirm these caps are good, although they are definitely bad if blistered or leaking at the ends. Old caps can weaken punch, volume, bass response - or show no audible signs at all yet fail in seconds. If this happens it can burn up the power transformer - an expensive repair.

If you don't know if either of those amps has had those caps replaced in the last 10 years or so they should go in to a qualified tech asap. Because some techs don't point out service needs and instead just "fix amps, you should specifically request that work. At the same time voltages should be checked, power tube bias checked and adjusted if necessary (always adjusted if the power tubes are replaced; power supply and screen resistors replaced with metal film; pots, jacks and tube sockets cleaned and lubed; and tension of tube sockets check/retensioned if necessary.

The resistor replacements are upgrades that are better for the amp and don't affect value; the rest is normal service done at roughly 15 year intervals.

Hope that helps -

[Tom Gorr]

I bought a 72 BMR with a matching fender 2x12 cab with Jbl K120s. About $1000 in it which isnt much considering the vintage matching package.

Prefer my $100 Peavey Heritage VTX 2x12 with Scorpions for very nearly every application especially steel guitar.

That said, I wanted a grab and go amp for six string electric jams so I built a new front plate for the BMR so it could fit 2x8" speakers and I went with Jensen MOD 8s because they were 20 bucks each and the written description sounded about what I was after.

Surprisingly I enjoy both the cleans and dirt pedal tones in the 2x8 mini combo config. Mission accomplished. Its a grabngo amp for 6 string electric.

[Brad Sarno]

. . . Is it wise to make big enough changes to make this a gigging steel amp?

DON'T!!!

That is a special amp, and that smaller output transformer is a very special and magical part of that series of Fender amps. It already is a great steel gigging amp. The only wise mods to these amps is to "blackface" the output section around the phase splitter and power tubes. Fender under the ownership of CBS in the very late '60s made some weird and arguably undesirable mods to this section that are VERY easily converted back to a mid-60's blackface design. To me, the blackface output section is ideal, musical, tried-&-true. But even if you don't mod that thing at all, it's gonna be a sweet singing amp head. But for sure DON'T beef it up. Just run it thru a JBL and enjoy the magic. That should be plenty loud for most gigs. If you feel like it runs out of clean headroom, just move the speaker closer to you to increase the perceived volume/loudness.

Keep in mind that this head is virtually the exact same amp as a Vibrolux and a Pro-Reverb. They compress so smoothly and musically and very gently delve into a nice overdrive when pushed. Just work the amp as it is. They're so special. I have and use a '68 Bandmaster Reverb just like it, and it's a gorgeous sounding steel amp into my old JBL D130.


B

[Tom Gorr]

Brad, since we are on the subject... A few ?'s for you...


1. What exactly does the blackface mod change in terms of feel and tone?

2. My reverb knob amplifies both presence and reverb until about 3.5 on the dial at which it squeels like a stuck pig except two octaves higher.

3. I have plugged in JJ 6v6s in place of the original Blackplate RcA 6L6s and frankly.. The 6v6s bring something to the table with this amp, but you do need to run an 8 ohm speaker load to impedance match or it is not great. I would say... More musical low end, smoother more compressed mids, yet clear highs. I have no idea how the ones I plugged in are biased.. At least half the benefit is I can turn volume from 3.5 up to the 5 sweet spot at same apparent spl levels and get more tube amp OD response.


4. EQ. I run about V5 T7.2 M7 B4 on vibrato reverb channel. That is for a guitar with classic 57 HB type pickups.

[Jim Sliff]

1. What exactly does the blackface mod change in terms of feel and tone?

2. My reverb knob amplifies both presence and reverb until about 3.5 on the dial at which it squeels like a stuck pig except two octaves higher.

3. I have plugged in JJ 6v6s in place of the original Blackplate RcA 6L6s and frankly.. The 6v6s bring something to the table with this amp, but you do need to run an 8 ohm speaker load to impedance match or it is not great. I would say... More musical low end, smoother more compressed mids, yet clear highs. I have no idea how the ones I plugged in are biased.. At least half the benefit is I can turn volume from 3.5 up to the 5 sweet spot at same apparent spl levels and get more tube amp OD response.

1. Without getting too technical - The primary change is to the phase inverter and bias circuit, allowing the output tube bias to be adjusted to the optimum setting sound-pwise for the specific tubes installed. The later circuits either adjusted only one side in order to :balance" the bias or worked in a "seesaw" manner, the point being to have them match. The purpose was to allow mismatched tubes to be used and even the bias out.

But Fender's "ideal" bias settings are on the cold side, partially for extended tube life but also to "prevent distortion" - but so cold the amps tend to lack punch and response,,,and much of the warmth. When they were new the tubes produced at the time tended to sound at least "OK" with a older bias. but most production tubes today sound thinner/weaker when biased cold.

As tubes are usually purchased nowadays in matched pairs, and with the wide variety of bias settings necessary to get somewhat similar sounds when swapping power tubes, it's FAR better to have adjustable bias (although some modify amps to both adjust the bias and have a "seesaw" balance control so mismatched tubes can still be used. Not very common, however)

2. Take it to a tech. You can try replacing the V3 Reverb driver tube with a new 12AT7; if that doesn't fix it try replacing the V4 reverb recovery/gain tube with a new 12AX7. Either might fix it, but what you're describing is not usually a tube issue alone. If the amp needs some service anyway you might as well have this problem checked out at the same time.

3. Definitely take it to a tech. NEVER change the type of tube without a bias adjustment.. And 6V6's are running in Fender amps at plate voltages that are already way over spec even in amps intended for them; they may be redplating in the Bandmaster regardless off the impedance change.

The plate voltage HAS to be checked when installing them in place of 6L6's and should be checked every time the bias is adjusted. There is still adjustment done for sound, but setting the bias without knowing the plate voltage is an unsafe guessing game.

Not only the bias will need to be adjusted - you may need to have a different rectifier tube installed and other minor changes made.

Very often the impedance change is a "technically correct" thing that doesn't need to be done and may sound better the other way.

[Tom Gorr]

Thanks Jim.

One thing is I specifically am using the JJ 6v6 because it is designed to use as a 6L6 replacement for voltage tolerance.

Its not redplating. Not even burning the stencil graphics off. From past experience if power tubes are they are too far off optimum they sound not great and these sound terrific so I am thinking I lucked out on the match.. But yeah.. Would be at least nice to have the blackface bias mod and set these to optimum.

I replaced the reverb driver and recovery tubes to no change in squeeling so I think tbere must be local feedback coming from somewhere. When I look at the schematic..cannot believe they all dont feedback
Hoping Brad Sarno or Ken Fox may have encountered this before.

[Brad Sarno]

6L6's belong in that amp.

[Tom Gorr]

6L6's belong in that amp.

I do not disagree with that statement with the 1x15 D130F cab I have.. (You also recommend).. Sounded great but the cab is an Early Traynor bass cab and while it is a great match musically with the RCA 6l6s it doesnt look good so it sits in storage till I find a matching 1x15 guitar cab. Haha. Gear only sounds as good as it looks

My matching 2x12 with the k120"s sounds much better with the JJ 6v6s which some say are a 6L6 sounding 6v6. Guaranteed this is an amazing combination.

Brad do you have time to walk through my questions.. Anything to add on Jim's points?

[Jim Sliff]

I replaced the reverb driver and recovery tubes to no change in squeeling so I think tbere must be local feedback coming from somewhere.

The amp needs to go to a qualified tech.

Voltages need to be checked top see how close to spec it's running. But reverb squeal, if not caused by a tube or reversed reverb tank wires, could be caused by a loose coil in a tiny reverb tank transformer (not repairable - the tank is simply replaced), or the reverb transformer that's mounted to the chassis, or a faulty resistor or capacitor in the reverb circuit, a bad solder joint, or dirty/corroded tube sockets that are not making full electrical contact.

There are debugging procedures that most good techs can work through in 2030 minutes.

[Tom Gorr]

Thanks Jim.

Reverb tank is brand new... The amp was missing it and the tech who had gone thru the amp sold it to me on a promise to send me a new spec reverb tank. Plugged in or not it still squeels at same place on dial.

If it is a failed resistor or cap there, that is something I can fix myself assuming I dont get zapped from the B+..

I would do my own tech work if i wasnt afraid of dying from B+ voltage accidents. I can read schematics and solder, and have compared and contrasted at least 10 amp circuit schematics ranging from classic marshalls and fenders, to complex amps like multi channel boogies. I modded a preamp once and fixed a few inoperable pedals.

Is it enough to unplug amp while it is on to drain the power supply filters? I could poke around with my 300 dollar digital multimeter.

[Cartwright Thompson]

6V6’s in that amp? Really?

[Tom Gorr]

6V6’s in that amp? Really?

Its a high voltage Deluxe Reverb now!

[Jim Rossen]

What gives me piece of mind about B+ shocks is to discharge the power supply filter caps using a shorting lead with a 1K 10W power resistor (after unplugging the amp!). One insulated lead has an alligator plug clipped to the metal chassis. The other insulated lead is touched to convenient power supply filter cap nodes on the circuit board. I don't think you need to short each cap, a couple few will do. If you can't identify the nodes, you probably should not be working on the amp. The resistor just reduces arcing when contacting the hot node.

Jim