67-68 Bandmaster

[plaush]

Greetings, a general question for any and all. I have acquired a 67-68 Fender Master and I intend to make it sound heavenly. Before I proceed, does any body have any tips or advice?

[Amp Kat]

That amp IMO is one of the sweetest amps Leo ever made and they really sound awesome when working right. If it is original and has the original gold paper E-Caps then I would replace them and especially the ones under the hood and the Cathode bypass caps. If it's dirty or has filth, clean it up good and get all of the dust out. Try not to use hard chemicals on it as it can screw it up especially the faceplate but you can get another faceplate from Mojo if it's bad. Many change the blue coupling caps but if they still hold the DC well I keep them in because of the vintage tone they possess and the replacements depend on you're budget but the Malory 150 series works well in those. Try to keep the wiring routing in tact exactly like it is but if the pots are scratchy you may have to take them out and clean them. New cap job and that amp will likely outlast you. Then again if you really want it done right you could ship it to Bruce at Mission and let him rejuvenate it for you and it would be golden. I would consider it but good luck either way.

[Gibsonman63]

... and while you are at it

While you have it apart, make sure that switching jack contacts are clean and making contact with no instrument cable plugged in, put some quality tubes in her and set the bias.

If you have the original cabinet and speakers and the speakers are original and have not been reconed, you may want to pull them and put them away and put some high quality replacement speakers in there. The amp will be worth more on th collector market with original speakers if you ever want to sell it.

Of course don't forget about the lethal voltages in these amps stored in the power supply filter caps. These guys really aren't kidding with the warnings

I have a '65 with the 2-12 cabinet and tilt-back legs that looks cool and sounds great. I use both channels and switch externally with an A-B switch, so I can crank up the normal channel for leads. A Boss DS-1 works well with this amp if you really want to push it hard.

Hope it helps.

[plaush]

Doh!!

Greetings, a general question for any and all. I have acquired a 67-68 Fender Master and I intend to make it sound heavenly. Before I proceed, does any body have any tips or advice?

Thanks for the replys. I hear good things about mission amps so I wouldn't hesitate to send this thing to Bruce except for that I need something to keep me out of trouble.

[Dave Curtis, dB AudioTech]

Does it still have the 2-wire AC cord? Replace it with a 3-wire grounding cord, disconnect the polarity switch and rewire the power switching; the neutral should go directly to one wire of the primary winding of the power transformer and the hot should go through the fuse, the switch and then to the other wire of the primary winding. That's the first thing you should do. Then replace all the electrolytic caps, don't forget the bias cap; use a 100uF/100V part there.

Also, keep in mind that a great many Fenders had the convenience AC outlet wired backwards; the wide slot should be neutral and the narrow one is hot.

[plaush]

Does it still have the 2-wire AC cord? Replace it with a 3-wire grounding cord, disconnect the polarity switch and rewire the power switching; the neutral should go directly to one wire of the primary winding of the power transformer and the hot should go through the fuse, the switch and then to the other wire of the primary winding. That's the first thing you should do. Then replace all the electrolytic caps, don't forget the bias cap; use a 100uF/100V part there.

Also, keep in mind that a great many Fenders had the convenience AC outlet wired backwards; the wide slot should be neutral and the narrow one is hot.

Good idea. Since I am currently more of an electrician than an amp tech I'm cool with what your telling me. I have possession of a new cord and I'm foaming at the mouth, whet with antcipation of starting this project.

I'm getting a kit from Torres Engineering. I figure it's better have all the parts right there when I start. Down the road when I'm more familiar with amp repair/building I will purchase parts seperately. Hopefully if I take my time this thing will work out nice. I do have an electronics background so I'm not starting without experience soldering, reading schematics etc. Thanks for your reply

[Regis]

Does it still have the 2-wire AC cord? Replace it with a 3-wire grounding cord, disconnect the polarity switch and rewire the power switching; the neutral should go directly to one wire of the primary winding of the power transformer and the hot should go through the fuse, the switch and then to the other wire of the primary winding. That's the first thing you should do. Then replace all the electrolytic caps, don't forget the bias cap; use a 100uF/100V part there.

Also, keep in mind that a great many Fenders had the convenience AC outlet wired backwards; the wide slot should be neutral and the narrow one is hot.

Dave is correct, read here.

[plaush]

Dave is correct, read here.

Very cool. Thanks for the info. I believe what we are referring to is a polarized receptacle in which case the small slot is should always be the "hot" and the larger slot is the nuetral.

I wasn't sure about what to do with the capacitor. At first glance I thought maybe the cap would help with noise. It seems like it would just as simple to bypass the ground switch altogether. Is there a reason I do not here more about the switch being bypassed?

[Bob M.]

Bandmaster...

These amps can sound good but also can sound underpowered. Generally speaking, there is one less stage in this amp's design than in the combo/reverb Fender amps, hence, it's really important to get the phase inverter stage working up to maximum efficiency. Tighten the tolerances on any drifted components by liberal replacement and remember, Fenders love to eat 12AT7s. Good luck; you'll have alot of fun with this amp!

Bob M.

[plaush]

These amps can sound good but also can sound underpowered. Generally speaking, there is one less stage in this amp's design than in the combo/reverb Fender amps, hence, it's really important to get the phase inverter stage working up to maximum efficiency. Tighten the tolerances on any drifted components by liberal replacement and remember, Fenders love to eat 12AT7s. Good luck; you'll have alot of fun with this amp!

Bob M.

So an AT7 instead of AX7 for the phase inverter? Always?

[Bob M.]

plaush,

I was speaking extemporaneously; Refer to your Fender book/CD of schematics. All the later Bandmasters, of the same era as yours, used an 12AT7 in the PI position: AB763, AC568, AD1269, even the odd-duck Bandmaster Reverb AA270/TFL5005D. I certainly would try a (known-good) 12AT7 first, unless you have a very solid reason to try another tube. The earlier Bandmasters: 5E7, 5G7, 6G7, 6G7-A used either a 12AX7A or a 7025. On the tweed amps, this wasn't a long tailed pair PI so all bets are off there. Maybe the BF/SF preamp with the early 60s PI will be perfect for what you're trying to accomplish. Of course, this all depends on how you want this amp to sound, what you want it to do. I don't think there is such a word as 'always' in the world of point-to-point open architecture design. There wasn't in Leo's world.

Here's some info for you about Bandmaster history:

GGJaguar's Guitarium and Ampeteria Project Bandmaster

Bob M.

[Dave Curtis, dB AudioTech]

Very cool. Thanks for the info. I believe what we are referring to is a polarized receptacle in which case the small slot is should always be the "hot" and the larger slot is the nuetral.

Yes. Check yours and let me know if it's ack-basswards; Fender finally caught on by the late 70s, if memory serves correctly. My '76 was backwards.

I wasn't sure about what to do with the capacitor. At first glance I thought maybe the cap would help with noise. It seems like it would just as simple to bypass the ground switch altogether. Is there a reason I do not here more about the switch being bypassed?

I usually disconnect it altogether. I've re-used the one in my Pro Reverb to open up the negative feedback loop...

[plaush]

Yep, it sure was

Yes. Check yours and let me know if it's ack-basswards; Fender finally caught on by the late 70s, if memory serves correctly. My '76 was backwards.



I usually disconnect it altogether. I've re-used the one in my Pro Reverb to open up the negative feedback loop...

Hey Dave, update... I got into this thing and sure enough the wires coming in were wired to the polarized receptacle incorrectly. The wire was a 3 prong wire though. It was an older style 3 prong cord.

I bought the amp off of an HVAC mechanic I work with. He told me that another HVAC Mechanic we both know did him a favor and put the cord on for him. Maybe I should refrain from having the second feller do any HVAC work for me?

In any event I am replacing the cord with a proper one. I think I will just bypass the whole switch for now.

[Dave Curtis, dB AudioTech]

Hey Dave, update... I got into this thing and sure enough the wires coming in were wired to the polarized receptacle incorrectly. The wire was a 3 prong wire though. It was an older style 3 prong cord.

I bought the amp off of an HVAC mechanic I work with. He told me that another HVAC Mechanic we both know did him a favor and put the cord on for him. Maybe I should refrain from having the second feller do any HVAC work for me?

Well, he likely just wired the 'new' cord like the old one, and didn't check the polarity on the receptacle. That said, being a Master Electrician, I've seen some pretty bad wiring by HVAC guys. Be nice though; you might need your furnace worked on someday.

In any event I am replacing the cord with a proper one. I think I will just bypass the whole switch for now.

You can reuse it later for something else. It's just a hole-filler on my VT22 (for now)...

Have fun, and keep us posted.

[TimC]

I have a Bandmaster AB763 head that I did a few mods on. When I bought it the grill cloth had been replaced with one of a black plastic material so any collector value was shot. I used one of the blinded power tube holes to mount a tube rectifier. I had to add another small transformer for the rectifier heater supply. I changed the fixed bias to a cathode bias and used one of vibrato pot holes for a presence control pot. I kept the 6L6's as they sounded good as is.