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Bandmaster Reverb mods questions Electric Guitar Amplification
Old 4 days ago
  #1
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Bandmaster Reverb mods questions

I'm considering picking up a '69 Silverface Bandmaster Reverb (head, with a Tube rectifier I believe) from a friend of a friend as an alternative to the other newer 40w variants like the Blues Deluxe and its Reissue, or the Hot Rods, etc, for my main Clean sound for non-Baritone guitars.

I wasn't familiar with this model before last week, and in the brief reading I've done it seems quite similar to a Deluxe Reverb (w 6L6s), which has me wondering whether one could modify Channel 1 of the Bandmaster Reverb to essentially be a Deluxe Reverb?

Would it require a unique Transformer for each side? Would the impedence be the same in both modes? Also, what about adding the Dwell and Level controls to the Reverb circuit like those in the standalone Fender Reverb units of the era?

I'm sort of hoping I can franken-MOD this thing and end up with what's essentially a BMR head, a DR head (or a Princeton equivalent, maybe), and a Standalone Reverb unit all in the one big head case that the Bandmaster comes in...

What do you think? Would that or something very similar work? Dirty/Breakup/~20w on Channel 1, and Clean/Headroom/~40w on Channel 2, each with Reverb that has both Dwell and Level added, with a Tube rectifier and Tube Reverb circuit...?

That would sort out most of my Fender wants in one box, and save me the hassle and cost of owning a DR or Princeton *and* the BMR, and anything that saves that hassle is a good thing.

Thanks.
Old 4 days ago
  #2

It won't be a tube rectifier...

Sounds like you want to build two complete amps into that big head cab. It might be easier to just get two lunchbox amps. The 20w on one channel and 40w on the other channel isn't going to work - at best you'd be able to put a power-section mode on a switch.

Now, if you can find a Mesa TA-30, the engineers have set up all the relay switching to get multiple power levels to work.



-tINY

Old 4 days ago
  #3
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enorbet2's Avatar
It isn't difficult to get both channels working with one reverb section since that is all signal level operation where one only has to be cognizant of phase relationships, especially if both channels can operate simultaneously. That's pretty EZ. Power amp switching is by nature more complex and expensive as well as slightly more risky in 2-tube output. Some of that has to do with increased voltage and current levels but impedance matching is one more serious issue that needs to be addressed. I've modded amps like this before but making it instantly switchable can reduce its roadworthiness just by introducing critical switching. It's not at all trivial. It's far easier and more reliable to provide a PreAmp Out and switch between internal and an external power amp but of course that requires 2 speakers.

Personally I opted for a Class A 30 watt power section and tilt back legs placed in front of me angled up at my face, turning it into essentially a stage monitor... that coupled with a decent PA can play anywhere with sufficient headroom.for solid cleans and natural overdfrtive that won't melt your face. That works great and is ultra simple and reliable. FWIW it is trivial to mod a BMR to Class A at 15-30 watts depending on output tube choice.
Old 4 days ago
  #4
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Quote:
Originally Posted by tINY View Post
It won't be a tube rectifier...
The published specs say the Bandmaster Reverbs between 68-75 had Tube Rectifiers, at least those listed on Fender Guru and a couple of other spots online.

Are you saying that's incorrect?

The same sources say all of the other Bandmasters had a Solid State Rectifier... the non Reverberating heads and the Reverb versions before and after 68-75.
Old 4 days ago
  #5
Quote:
Originally Posted by RunnyKine View Post
The published specs say the Bandmaster Reverbs between 68-75 had Tube Rectifiers, at least those listed on Fender Guru and a couple of other spots online.

Are you saying that's incorrect?

The same sources say all of the other Bandmasters had a Solid State Rectifier... the non Reverberating heads and the Reverb versions before and after 68-75.


Interesting - I was under the impression that, after the brown-face amps, all the Fenders went to SSR.



-tINY

Old 4 days ago
  #6
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Quote:
Originally Posted by enorbet2 View Post
.snip.
Okay. That's more troublesome than I'd like.

Thanks for the insights.
Old 3 days ago
  #7
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What about adding features to the Reverb of the Bandmaster, like the Dwell and Mix and its own Tone control like the 60s era Standalone Spring Reverb has? How time consuming and costly are those mods? I've not done that before, but I can follow instructions and know my way around pedals and guitar guts and soldering irons.

Lastly, if I were to buy a second Transformer - specifically the ones like used in the Twin (a common mod, apparently, for the wattage/headroom gain), is it any more complicated than just unhooking one and hooking up the other? Can I manually swap them back and forth (not hot-swap... but occasionally...)? Would it need rebiasing or any other adjustments when going from one to the other?

Thanks.
Old 3 days ago
  #8
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Quote:
Originally Posted by tINY View Post
Interesting - I was under the impression that, after the brown-face amps, all the Fenders went to SSR.
This one in this year range appears to be an exception, which I'm pleased to read.

Here's a source: BF/SF Bandmaster | fenderguru.com

Quote:
'68-'75 Silverface Bandmaster Reverb tubes:

V1 12ax7 = Preamp normal channel
V2 12ax7 = Preamp vibrato channel
V3 12at7 = Reverb send
V4 12ax7 = 1/2 Reverb recovery and 1/2 gain stage for vibrato channel
V5 12ax7 = Vibrato
V6 12at7 = Phase inverter
V7 6L6 = Power tube #1
V8 6L6 = Power tube #2
V9 GZ34/5U4GB = Rectifier tube
Old 3 days ago
  #9
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Quote:
Originally Posted by RunnyKine View Post
The published specs say the Bandmaster Reverbs between 68-75 had Tube Rectifiers, at least those listed on Fender Guru and a couple of other spots online.

Are you saying that's incorrect?

The same sources say all of the other Bandmasters had a Solid State Rectifier... the non Reverberating heads and the Reverb versions before and after 68-75.

Not sure where you're getting your info but the bandmasters did not have Tube rectifiers. Someone may have taken out the solid state and installed a tube but that's allot of work for nothing.

I've owned a Blackface bassman since 67 and its essentially the same amp minus the reverb or tremolo. Most band masters only had tremolo in the beginning. They added reverb to the silver face versions in the 70's and doubled the head cab size to accommodate the reverb tank.



The reverb and the tremolo do run on tubes which is likely the reason the bandmaster is rated 10W less then the Bassman. The extra tubes and wiring suck volume.

If you want to mod the amps there are a ton of variations you can do to them. The only one I did was to add a midrange knob to mine. Having a 3 band EQ lets you get those tweed tones.
Old 3 days ago
  #10
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enorbet2's Avatar
Quote:
Originally Posted by wrgkmc View Post
Not sure where you're getting your info but the bandmasters did not have Tube rectifiers. Someone may have taken out the solid state and installed a tube but that's allot of work for nothing.

I've owned a Blackface bassman since 67 and its essentially the same amp minus the reverb or tremolo. Most band masters only had tremolo in the beginning. They added reverb to the silver face versions in the 70's and doubled the head cab size to accommodate the reverb tank.

The reverb and the tremolo do run on tubes which is likely the reason the bandmaster is rated 10W less then the Bassman. The extra tubes and wiring suck volume.

If you want to mod the amps there are a ton of variations you can do to them. The only one I did was to add a midrange knob to mine. Having a 3 band EQ lets you get those tweed tones.
Sorry. OP is correct and you are mistaken. Many Bandmasters had tube rectifiers. I know this because I owned an Authorized Fender Service Center for over a decade and they sent me a massive loose leaf folder collection of all their schematics that I still have today. You can verify this easily by searching "Fender Bandmaster" and "Fender Bandmaster Reverb" and add 'schematic on the end of each. Look at the images for yourself.

You are also mistaken that "the extra tubes and wiring (associated with Reverb and Tremolo) suck volume". The difference of 10 watts is due to the fact that Bandmaster have GOBS of negative feedback. Look at the schematics of Silverface Bassmans vs/ a Bandmasters. You will see a feedback resistor from output to PI between 27,000 Ohms and 47,000 Ohms on the Bassmans where by contrast the Bandmaster has 820 Ohms. The gain structure of the PI stage somewhat compensates which is why the difference is only 10 watts but the Bandmaster sounds 'stifled" compared to a Bassman due to this heavy negative feedback and the alteration of damping factor. They do, as you noted, sound less loud but it isn't because of a lousy 10 watt difference.

If the addition of a Midrange control has you convinced that you can get "those tweed tones" I am not about to argue since it apparently, whatever name we put on it, pleases you, and that's what matters most. However there are a number of great sounding Tweed models that don't sport a Midrange control and some of the best ones only have a Tone control. The biggest difference Tweeds have in common is substantially less negative feedback than Black or Silver faced models - Tweeds BREATHE! and negative feedback is only one, albeit important, difference. They also tend to run in AB1 instead of AB2 configuration - closer to Class A, more responsive.
Old 2 days ago
  #11
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I stand corrected. The Silverface reverb model in the oversized cabs did have a 5U4GB Rectifier tube.
I was familiar with the smaller vibrato versions and didn't realize they went back to using a tube on those.

Both the Bassman and Bandmaster have so many different variations before and after CBS took them over.
I suspect many were instituted to simply use up the old parts.

I had a Blackface Bandmaster for a short time. I ran side by side with my Bassman and it didn't hold a candle to the Bassman for tone or power.
It broke up at much lower volumes and sounded like it had a blanket over the cab. I eventually dumped the bandmaster and picked up a second Bassman.
I ran the Silver face and Blackface Bassman together for a couple of years then got something else.

As far as mods go, I did try out some of the mods to give the Bassman a more Tweed tone but eventually reversed them except for the mid control.
I really wasn't impressed with the changes so why screw with something that works well. The blackface sounds killer with pedals and If I want a tweed tone I'll buy an amp that has it. I have been tempted to sell off my big stuff and downsize to something like a Tweed Bassman Reissue. Those are still one of the best sounding stage amps made and not so big that you cant get it in the trunk of a car.
Old 2 days ago
  #12
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My 68 drip edge Bandmaster Reverb has a rectifier tube. You also might want to play it a while before modding. Mine sounds really good to me stock
Old 2 days ago
  #13
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enorbet2's Avatar
There is no need to be squeamish about modifications when they don't lose the original. By this I mean ones that can be adjusted back to dead stock. A great example of this that also addresses what many consider the major problem with amps like Bandmasters, which includes a great many of both Black and Silver face Fenders and clones, is excessive negative feedback.

Look again at a Bandmaster schematic and see the 820 ohm feedback resistor from Output to the PI/Driver stage. If one installs a pot wired as a vriable resistance in series with that 820 ohm original, obviously when the pot reaches zero (0) ohms, it is effectively out of the circuit and the original massive negative feedback is in full effect. BUT now you have the ability to reduce that feedback by increasing the circuit resistance of the pot and feel/hear how that "opens up the sound", lets the amp "breathe".

Once you discover what level you like best you have many options, including replacing both the 820 ohm resistor and the variable pot with a single resistor of a value of A + B. One can also elect to add a Presence control so that you have a post preamp EQ.. or you can substitute it if you want to discover what happens when only some frequencies are suppressed..

If you think about it, this is often possible to accomplish by using an existing location or an internal trim pot so that it is easy to return to original with no lasting effects or evidence of alteration, if that's important to you. This sort of mod has huge effect and is extremely easy for anyone who even only knows whet end of a soldering iron to hold.

Personally I never liked stock Bandmasters but just this one easily reversed mod makes them much more musical and responsive. Since it can be done with minimal skill and understanding of electronics, with only YOUR EARS as judge, and can be done easily in a single afternoon, I highly recommend this minor chore. Even if you don't like it and return to dead stock you will have learned something valuable.
Old 2 days ago
  #14
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Indeed.

I happen to like the way they sound, so I'm not really looking to "fix" anything, per se, but I would like to explore various mods and add-ons like the Negative Feedback one you mentioned and at least adding the Dwell and Mix and Tone controls to the Reverb circuit, but those are just things in other Fender amps.

My initial curiosity about modding Channel 1 was just a passing thought. I've since moved on from worrying about the Bandmaster Reverb having a lower power mode. It would have been cool if there was a simple, cheap, and reliable way to make Channel 1 into (effectively) a Deluxe Reverb, but you've cured me of that whim.
Old 1 day ago
  #15
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enorbet2's Avatar
Well never let it be said that I "cured" anyone from experimenting with modifications on amplifiers. What I set out to do was to just influence people to do that with an eye to returning to stock oir at least the "wiggle room" to cure any unforeseen ills.

Here's a Biggy to consider that requires extensive planning but is highly rewarding AND gives one huge leeway on the Reverb circuit..

There isn't a great deal of difference between a Deluxe preamp section and a Bandmaster.preamp, and whether in phase or out, when combined they affect each other. This can be fortuitous. Neil Young famously finds some "sweet spot" where the interaction results in a dynamic response he now simply must have.

There IS a huge difference between Black/Silverface preamps and Tweeds, not the least of which is that in Black/Silver the Volume control immediately follows the tone stack while Tweeds have the Volume control first driving a gain and impedance matching limiter stage and THEN comes the Tone stack. The drive and response difference is immense but the Tweed Circuit requires an additional 12AX7. Where to get that? - One answer is gut the Reverb circuit and create a switchable, buffered FX Loop with the remaining tube socket. for post drive use of Delays, EQ, Volume Pedals, etc and an effective Master Volume that is only engaged when some device is plugged in the loop..

Then use the components gutted and an old amp head to create a dedicated external Reverb unit with any mods you like. I made my own design but the old fender Reverb unit design can be used especially if one pads the input down and has sufficient gain in the output to satisfy drive requirements at medium FX Loop levels. This also can be used to reduce noise often associated with Reverb circuitry. If planned properly it is possible to easily return to a pure Bandmaster tone and response and no additional chassis holes need be drilled..
.
Old 4 hours ago
  #16
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norbury brook's Avatar
 

I have the same amp a bandmaster reverb. Dumble now only does amp mods and he does an ultra phoenix version of the bandmaster which gives you what you're after. Give him a call :D


seriously though any amp tech can mod channel one for you. the difference between a deluxe reverb and bandmaster reverb normal channel is just a couple of different value caps on the tone circuit. the actual main circuit is exactly the same. 1.5k/25uf-25v cathodes and 100k plates.



MC
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