PBBPaul

One cab at a time. You can though, take two 8 ohm cabs as an example and plug a parallel Y adaptor into the 4 ohm tap. Or .... two 16 ohm cabs into the parallel adaptor and plug that into the 8 ohm tap. That's kinda what I figured, thank you. I actually do have a 1x15" 16-ohm cabinet loaded with an early 60s Rola and a 1x12" 4-ohm cabinet loaded with a Celestion V30 and thought that they would sound quite nice running together from a small head that I built. Since the resistance is so far apart, I see no way to run them in either series or parallel.

Myles, As a general principle; If an amp has a multi-tapped output transformer with 4/8/16 ohm taps, is it OK to simultaneously run say, a 4 ohm cabinet and a 16 ohm cabinet from the apppropriate taps? Or should one limit oneself to only one tap at a time? Thanks, Paul

Hi Myles, I've been gigging with my home-built "twin" amp that is based on an old Bogen PA amp chassis. It uses 7868 power tubes and I really love the sound of this amp. The 7868's seem to be fairly rare but I'd like to get a backup set. Do you have a reasonably priced source that you would recommend? Or do you have any kicking around the shop that I could buy? By the way, I was in the L.A. area last week and almost found the time to stop by and say hello. Unfortunately, it didn't happen. Perhaps next time. Thank you, Paul

Very interesting. Thank you.

I saw that one too. Here is the one I'm talking about: http://i7.ebayimg.com/03/i/03/07/d2/7b_1_b.JPGhttp://i11.ebayimg.com/03/i/03/07/8e/f2_1_b.JPG Hence my confusion.

Myles, Have you ever heard of an RCA variant of the 6L6 called a 7552? It seems to have a metal base with Coke-bottle shaped glass.

Myles, My current project amp has a 6EU7 in V1, a 12AX7 in V2 and a 6C4 in V3 with 6L6 power tubes. I have no experience with the 6C4 and the 6EU7 preamp tubes and I didn't find any real info in your tube primer either. What are the typical characteristics of these? If I want to replace them, what should I look for? I don't have a schematic but I assume that the 12AX7 is the phase inverter. Is it odd for it to be in the V2 position? By the way, I have this thing pretty well cleaned up now and other than some slight hum (my new caps aren't here yet), it sounds very good with a surprisingly nice, warm breakup from the GT 6L6C's that I popped in there.

Hey Myles, I picked up a new project amp - an old Bogen PA head from the late '60s or early '70s. For tubes, it has a 6C4, 1 6EU7, 1 12AX7 and 2 6L6s. Do you have any recommendations on the preamp tubes? I'm looking (of course) for warmth and a nice fat overdrive. Do you also have any recommendations or opinions on capacitors? I've used Sprague Atoms and Orange Drops before but found them to be a bit harsh. And last question, what's your opinion on these NOS Sylvania 6L6G's? Are you familiar with them? http://i1.ebayimg.com/02/i/02/e7/3f/5d_1_b.JPG

On the Tweed Bassman, you can bridge the inputs, just as on a Marshall Plexi (that has the same front end, as it was copied from this Bassman). You do not want to do this on a Tolex era Bassman though. Myles, I've been bridging the inputs of my mid-70's Bassman for most of the past ten years by running a short cable between input 2 on the Normal channel and input 1 on the Studio channel. I've never had a problem. What's the scoop?

Myles, I was just checking out the numbers on this old Bandmaster. My output transformer does not appear to be original. If I understand correctly, it should have a part number of 022..... but the part number is 0822848 and the EIA number is 606-641 which leads me to believe that it was made in 1966 when the amp bears a mfr date of January 1965 and all the other dates indicate 1964. So... How can I check this OT for load requirements and make sure that it is right. I haven't been able to find the part number referenced anywhere. Thank you as always. Paul

Thank you Myles. I have one other question. I'd like to jumper the two channels of this Bandmaster like I do with my Bassman but the sound is really strangled when I do so. It sounds like the two channels are out of phase. Is that normal? Is there a mod to fix that? It would seem like it would be a fairly simple thing to do. I found this mod: http://community.webshots.com/photo/63936117/66383305LaywDw but I don't care if I have tremolo in both channels. I just want them in phase. Thanks again, Paul

Myles, I am considering using 3 10-inch speakers with my '65 Bandmaster. The amp is rated for a 4-ohm load. I've read that these older Fenders are designed to handle a 50% impedance load variation in either direction. Is this true? The Speaker and Extension Speaker jacks are wired in parallel which leads me to believe this but I thought I'd check with you first. If I use 3 8-ohm speakers in parallel, I'd get a total load of 2.67 ohms. I realize that this will tax the power tubes but is there any risk to the output transformer? What is your recommendation for a 3x10 speaker setup? 2 16-ohms and a 8-ohm will give me a total load of 4 but I'd like to keep the speakers matched if I can. Thanks, Paul

Paul, What the amp was done with originally, was conventional everyday solder as you find in most electronics stores. I'd steer clear of silver solder, sure it is great, but required higher temperatures to work, and this can damage other components nearby. Good enough, thank you. I have some of each kicking around. It's my understanding that the caps don't have to be quite exact replacements. Below is what is in the amp currently and what I can find for replacements. Can you tell me if this will work OK? Should I replace the molded caps as well as the electrolytics? Power supply filters (under the cover): Current: 20uF @ 525VDC X 3 70uF @ 350VDC X 2 Replacement? 20uF @ 500 Volts, Sprague # TVA1906 80uF @ 450 Volts, Sprague # TVA1716 On the board: Current Electrolytics: 25uF & 25uF @ 25VDC X 2 25uF @ 25VDC X 1 Replacement? 25 uF @ 50 Volts, Sprague # TVA1306 X 5 Onthe board: Current molded: .1uF 400VDC X 3 .1uF 200VDC X 1 .047uF 400VDC X 3 .1uF 600VDC X 2 (These are not original) Replacement? (Orange Spragues) .1uF @ 600 Volts, Sprague # 715P10496L .1uF @ 200 Volts, Sprague # 715P10492L .047uF @ 600 Volts, Sprague # 715P47396L .1uF @ 600 Volts, Sprague # 715P10496L By the way, I was pleasantly surprised to discover some unused GT6L6S' in my tube box the other night. They sound great in this Bandmaster (except for that bad distortion when cranked). Thank you again, Myles.

Myles, As I'm contemplating doing the recap job on my Bandmaster, it occurred to me, what's the best solder to use for max conductivity? I should know this from all the hours I've spent with a soldering iron in my hands but I don't. Is silver solder better than the tin/lead? Thanks again, Paul

Paul, The Bandmaster was designed for it's partner 2x12 cabinet, and yes, it is a 4 ohm load expectation. I'd first check all the preamp tubes, it sounds like ocillation issues. The caps may also be old and dry, so shot. Your power tubes are probably shot, and at the least, check the bias, and on your amp, look for at least 28 milliamps per tube. I'd also check those power supply caps under the cover on the chassis. Lift one end of each cap and test, or, since you will go to that much trouble to check, I'd just replace them. 30+ years on power supply caps is a LONG time. Thank you Myles, I have tried a couple of different sets of pre and power tubes with the same results. Currently installed are a set of lightly used Sovtek pre amp tubes that came stock with my Blues DeVille and a matched set of Groove Tubes 6L6's (C I think, the ones with the red base) with a 5 rating. I've just been goofing around so have not checked the bias yet. This amp has been recapped at least once but I'm not sure about the power supply caps. They look to be original so that is a great point. I'll test and/or replace them. Thanks again, Paul

Myles, I dont know if it can be said enough, but your help here is invaluable to us out here in the field. Thank you. As I mentioned not too long ago, I recently picked up a project amp: a 1965 Bandmaster. I plan on using it in a duplicate of the wonderful Bassman centered rig that I have now. While cleaning it up and playing with it, Ive uncovered a couple of issues that I wonder if you could help with. First, on the Vibrato channel (which I plan to use) - If I have the bright switch on and crank the treble past 7 or so, I get a terrible screeching noise. I have thoroughly cleaned both the switch and the pot but the issue is obviously elsewhere. Where do you think I should start? The second issue is a distortion that occurs when I hit the amp hard at higher levels (typically 5 and above). Its not a nice distortion, more like a slight buzz and comes in and out suddenly rather than gradually. It happens especially on the lower notes and big chords. Any ideas? Other than these two problems, the amp is wonderful sounding. Im currently running through a single Celestian 12 but will likely be moving to a pair of tens in the future. This brings up one last question, The specs I have found for the amp (here BTW: Fender Field Guide ) indicate that it is designed for a 4-ohm load. Is there any way that I can verify this? Thank you again for all of your help. The Tube Primer is outstanding by the way. Paul

Myles, I just picked up a 1965 AB763 Bandmaster. What do advise for getting the most possible warm, clean headroom out of it? The tubes that came with it were all shot (probably during shipping) so I just put in some that I had laying around and even with those, it sounds amazing. Dead quiet all the way to 10 (after a good cleaning). Anyway, I'd like to replace the '70s Bassman that's the center of my rig now with this amp so I'd like to get the most output possible without sacrificing the tone. Thank you, Paul

Myles, I have an original Ampeg Reverberocket (1962?) that needs some help. I believe that my preamp tubes are bad (they are original). I had it retrofited a few years ago to take 6L6 power tubes due to the lack of availability of 7591's. I had it re-capped as well. Now it will occasionally work for a few minutes before shutting down altogether. I don't have it in front of me but I believe that the pre tubes are 6SN7 and/or 6SL7. Do you have any advice on where to get these and which are best? Thank you as always, Paul