Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dbishopbliss on September 19, 2013, 11:31:41 am
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I would like to add channel switching to the AB763 ('67 Bandmaster) amp I am rebuilding. I have been told that I could use the relay boards for this. I have read the relay board pages, but I still don't understand how to use them.
Is there a schematic somewhere? If not, can someone describe how to add channel switching to an aB763 circuit? I will draw the schematic for confirmation.
Thanks.
David
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Have you considered just using an A/B/Y switch?
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That's too easy. :-)
I wasn't really planning on doing channel switching. However, in my first post to this forum (http://www.el34world.com/Forum/index.php?topic=15946.msg154996#msg154996) Eleventeen and Willabe made it sound as if using the relay boards was fairly simple. If its more complicated, then I don't really need channel switching. I'm a set it and leave it kind of guy.
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I have read the relay board pages, but I still don't understand how to use them.
Is there a schematic somewhere?
I wasn't really planning on doing channel switching.
There's a schematic in the link I posted for you in your 1st thread.
What don't you understand about using them? If you just want to learn or understand how they work, nothing wrong with that. Just ask your questions.
I would like to add channel switching to the AB763 ('67 Bandmaster) amp I am rebuilding.
If that amp is a black face I would not drill any holes in it, unless it was already chopped up. (I know that Fender sold to CBS in 65 but they (CBS) did build BF amps until they used up all the stock they had for them, so you can have a 67 BF.)
I think Sluckey's right about using an A/B/Y box if you just want to switch between channels. The Y setting would give you both channels at once for a boost.
You don't really need channel switching for this. Channel switching is needed for more complicated circuits.
Brad :icon_biggrin:
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That's too easy. :-)
Exactly. It's cheaper too.
Using the relay boards is fairly easy, but not as easy as the A/B/Y switch. If there was something you could switch on that amp with a relay board that you could not switch with the A/B/Y switch, I'd say go for the relay.
I'm thinking when you say channel switching, you want to do something with a footswitch that would simulate moving your guitar cord from one input jack to another input jack. That doesn't get any easier than the A/B/Y switch. Plus, with the A/B/Y switch you can have either channel or both channels selected.
I'd sure just keep it simple.
EDIT... You should post your schematic of this amp so people will understand you're not talking about a real AB763.
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You should post your schematic of this amp so people will understand you're not talking about a real AB763.
Well that's a horse of a different color then.
Brad :laugh:
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Many ways to skin a cat. Using a relay or 2 is no different than adding a mid boost switch or a fat switch. Any switching. In the case of the common fender 2 channel and making use of both the A/B/Y is the way to go.
Relay was confusing to me to begin, but once it clicked it opens up a whole other world. Pretty cool to be able to step on a pedal and change the amp circuit. That is the way I think of relay. Sometimes I am tweaking and I find a couple of different cap/resistor combinations I really like. If I want to keep both and switch them with a pedal the relay is the deal. Plus, learning how to use them is kind of cool to me.
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Relay was confusing to me to begin, but once it clicked it opens up a whole other world.
No pun intended, right? :laugh:
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Relay was confusing to me to begin, but once it clicked it opens up a whole other world.
No pun intended, right? :laugh:
None intended, I guess I am just a punny guy. :laugh:
Seriously, IMO it is well worth the time to learn to implement a relay or 2.
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I will stick with an A/B/Y box for now.
The amp is a '67 blackface bandmaster, but it was already hacked up. The power tubes were rewired for EL34's. It had some sort of master volume installed. It had a push pull pot that was supposed to add an extra gain stage. The tone circuit was supposed to be a "brown sound" whatever that means. All of these changes were made without really knowing how to solder so there were intermittent sound issues, hum issues, not to mention you could only play it while standing on a rubber mat, otherwise you would get shocked.
While I probably "could" have reused the original parts, I decided to go with an all new turret board, new pots and new sockets. The originals were in bad shape. Some of the lugs were cut, they had lots of flux on them, etc. In addition, the enclosure has a big hole in the grill, the tolex is peeling off, etc. Not to mention, this thing was really grimey. Lots of dirt and grease on it. You have to wash your hands after touching it. While there may be some purist out there, I'm not feeling bad about making this thing a little more modern.
Below is a shot of the guts before I started cleaning things up.
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The power tubes were rewired for EL34's.
You'll burn up the PT on that amp sooner or later running EL34's. They draw 2x the heater current than 6L6's do.
you could only play it while standing on a rubber mat, otherwise you would get shocked.
Put in a 3 wire power cord if you haven't done so yet.
Brad :icon_biggrin: