John Mcintyre Fender Bassman Bluesmaker Mod

[DrNomis]

Hi Fellow FSBers, I thought I would post these PDFs just in case anyone was interested in them, these are details for modding the Fender Bassman into a great amp suitable for Blues...enjoy:

[modman]

Hi DrNormis,
Yep I have that mag somewhere which just describes how to convert a Bassman into a Marshall Amp with a few extra tweaks.

If I recall it all correctly,, I found it rather disturbing that the article makes NO mention of the fact that EL34's need a lot more heater current than 6L6 and that means a new HT transformer or a second Filament transformer which complicates things and ups the cost by a considerable margin.
I'm not up to speed on all the details of Bassman/Marshall Amp models but I was warned years back that the mod may cause headaches with Bassmans.

Just thought I'd mention the fine print.

Actually the Prince of Wales looks like an interesting project as I do have a 6V6 Amp sitting idle,,, but damn it,,not enough time to do all these things.
Phil.

[DrNomis]

Hi DrNormis,
Yep I have that mag somewhere which just describes how to convert a Bassman into a Marshall Amp with a few extra tweaks.

If I recall it all correctly,, I found it rather disturbing that the article makes NO mention of the fact that EL34's need a lot more heater current than 6L6 and that means a new HT transformer or a second Filament transformer which complicates things and ups the cost by a considerable margin.
I'm not up to speed on all the details of Bassman/Marshall Amp models but I was warned years back that the mod may cause headaches with Bassmans.

Just thought I'd mention the fine print.

Actually the Prince of Wales looks like an interesting project as I do have a 6V6 Amp sitting idle,,, but damn it,,not enough time to do all these things.
Phil.

Yeah, I was thinking that too, you probably need to replace the original output transformer as well, I thought it was a bit strange that he didn't mention all that in the article, maybe he was on a deadline or something....

[modman]

It looks like John McIntyre's taken advantage of the reserve heater current capability inherent in Blackface and Silverface Bassman 50's. Fender used a transformer that can easily supply 2 x 6L6 and 6 x 12AX7 (7025) heaters, so there is enough heater current available for 2 x EL34's and 3 x 12AX7's with only a small extra current draw, resulting in a small increased risk to the transformer.

Fender 50 watt mains TX can supply up to 6 x 12AX7 @ 300mA (1.8A) + 2 x 6L6 @ 900mA (1.8A) = 3.6A total heater current vs Bluesmaker's 3 x 12AX7 @ 300mA (900mA) + 2 x EL34 @ 1.5A (3A) = 3.9A total heater current.

Modern transformers in commercial valve/tube amps generally have less current reserve....to save manufacturing cost. It is not a good idea to simply replace 6L6 output valves with EL34 or 6550 types without knowledge of the currents involved.

[phatt]

Hi Blackbunny,
Tar mate ,,, you obviously know more bout this than me but I think messing with these things can quite easily end in tears for the novice ,,Unless (like you) You know how to read between the lines and bring it all together.

Myself having been on the (I would not have a friggin clue how a valve amp works) End of these things I can clearly see that it can be very misleading when some half witt guru geek says,, oh you can turn any amp into a marshall,,, just add water and smoke some RockNRoll weed and then anything sounds wonderful.

(Adding also,,,Make sure the Valves have Gold print and are at least 60 years old )

I would erk at the idea of altering any kind of old Bassman Amplifier when it makes more sense to sell it and purchase a Marshall instead
(Do we have a dumb dumb emoticon?)

Interesting that you mentioned output transformer as well,,,,,

Yes I agree!! They are different and DO alter the Final outcome.
cheers mate,,, Phil.

[DrNomis]

I reckon it would be a different story if you were to build the Bluesmaker circuit completely from scratch, that is, instead of ripping apart a Fender Bassman, make a complete new chassis and cabinet, use an output transformer specifically designed for two EL34 tubes, and power the amp with an appropriately rated mains transformer...

Once the circuit is all built up and operating correctly, then you could tweak it a bit...

[blackbunny]

I would erk at the idea of altering any kind of old Bassman Amplifier when it makes more sense to sell it and purchase a Marshall instead
(Do we have a dumb dumb emoticon?)

I remember that Silverface Fenders were cheap, easy to find in pawn shops and music shops, and not at all hip when I was travelling around the US in the mid 90's. It's a wee bit ironic that Mr McIntyre made a name for himself by modifying undesirable "dirt cheap" SF bassman heads to be more like the "classic" tweed Bassman that was enjoying a revival at the time.

The Bluesmaker circuit takes elements from the '91 Fender Tweed Bassman reissue / early tweed Bassman / JTM45 Marshall circuits. The input signal is fed to two preamp stages in parallel - like using a patch lead between the inputs - one input stage has increased gain while the other stays clean and bright, and there is a blend circuit. Then to a classic Fender tweed / Marshall cathode follower, and a driver/ phase splitter that is a tweaked Blackface with looser damping, using a 12AX7 for a looser, more vintage overdrive.

I don't think too many people here in Australia would be hacking up SF Fenders these days, judging by the hefty prices they are selling for on eeeeBay. Strange to think that 20 years ago they were cheap and un-hip.

The cork-sniffers will still pay ridiculous prices for anything Blackface of course, even crappy reissues like the Fender BF Deluxe and BF Twin Reissues. I've fixed a lot of those....no, it's not the PCB that's the problem, it's the cheap asian caps and resistors. And the Sovtek output valves don't help either.

I'm a crusty old bloke these days....(sucks teabag)....I wish people wouldn't use really cheap components in valve amps with 450 VDC power supplies. (shuffles off to bed)

[AL]

Thanks for the post. Looking forward to sitting down and reading through it this evening.

AL

[bhill]

And we will leave out the fact that many artists used the Bassman in the studio for guitar. Just plugged into the normal channel and wailed. And we can overlook the JTM 45 was originally a Bassman built upside down.

Leaving out that changing things this way is pushing the transformers to the ragged edge, why would you want to lose the Bassman sound in the first place. If you want a Marshall, sell the Bassman to someone who wants it and buy one.

And yes, I am one that likes the BF amps. Not a cork sniffer, I have had a '65 Bandmaster since 70 and just finished rebuilding a '67 Bandmaster my other half snuck out the shop I help out at and conspired with some so called friends to sneak it home. Gotta keep a woman like that.

[blackbunny]

And yes, I am one that likes the BF amps. Not a cork sniffer, I have had a '65 Bandmaster since 70 and just finished rebuilding a '67 Bandmaster my other half snuck out the shop I help out at and conspired with some so called friends to sneak it home. Gotta keep a woman like that.

I'm a BF nut myself, and I'm mystified that people would want to hack them up. I love to restore them, rather than "hot rod" them, but I guess that's up to each individual owner.
At the time that John McIntyre originally published his design, Silverface Bassmans were cheap and not very desirable, so I hope that most of the Bassmans that were Modded were Silverface, not BF.

Most Silverface amps can also sound terrific with new filter caps and plate resistors, and the right choice of speakers.

My reference to cork sniffers was a (not very clever) jibe at those who think they're getting a "Blackface" Fender by buying a modern '65 Twin or Deluxe reissue.
The modern ones can be greatly improved by replacing a few power supply filter capacitors and some coupling caps, which will help get them into the BF ball park.

I would love to see a photo of your '65 and '67 Bandmasters, and your better half sounds like a rare treasure indeed.

[DrNomis]

And yes, I am one that likes the BF amps. Not a cork sniffer, I have had a '65 Bandmaster since 70 and just finished rebuilding a '67 Bandmaster my other half snuck out the shop I help out at and conspired with some so called friends to sneak it home. Gotta keep a woman like that.

I'm a BF nut myself, and I'm mystified that people would want to hack them up. I love to restore them, rather than "hot rod" them, but I guess that's up to each individual owner.
At the time that John McIntyre originally published his design, Silverface Bassmans were cheap and not very desirable, so I hope that most of the Bassmans that were Modded were Silverface, not BF.

Most Silverface amps can also sound terrific with new filter caps and plate resistors, and the right choice of speakers.

My reference to cork sniffers was a (not very clever) jibe at those who think they're getting a "Blackface" Fender by buying a modern '65 Twin or Deluxe reissue.
The modern ones can be greatly improved by replacing a few power supply filter capacitors and some coupling caps, which will help get them into the BF ball park.

I would love to see a photo of your '65 and '67 Bandmasters, and your better half sounds like a rare treasure indeed.

I reckon the best bet would be to leave a stock Bassman alone and just build the circuit up from scratch in a new chassis, using new components, etc, that way the Bassman stays stock (keeps it's value) and you get the satisfaction of building an amp from scratch....


Wouldn't mind having a go at building one from scratch myself, would probably learn a few things in the process too.....

[electrosonic]

I'm a BF nut myself, and I'm mystified that people would want to hack them up

In 1993 when that was first published, Bassman heads were not considered vintage. They were not very expensive and people modded them without a second thought.

I think most people these days would see the value in keeping them stock.

Andrew.

[Aharon]

Wow,I still have the GPlayer mag in which was published.
Aharon

[dave_b]

Wow,I still have the GPlayer mag in which was published.
Aharon

I still have that issue as well. I still have my SF Bassman, too. ...and yes this is an old thread. I didn't do that rebuild, but I did do some things.

I paid $60 for my amp around 1989, so modifying it was a free-for-all as far as I was concerned. I did the EL34 conversion without knowing about the additional current requirements. This is pre-Internet, and I think I picked up the info from one of the Aspen Pittman books. I know I spoke with Ken Fischer about it and he made no mention of it being an issue. I asked him a ton of questions that evening, so it seems like he would have pointed out any risk of doing the conversion. Having said all that, I never gigged with the amp and it doesn't have a lot of hours on it in this configuration. I do tend to play it dimed, FWIW.

[chicago_mike]

I had a Bassman 100 and 135 and got both for like 100 each in the 90's. Now you can't touch them for 500...

Easy to work on and easy to learn on too.

[darkbluemurder]

I tried the Bluesmaker circuit in one of my modded Marshalls and found it rather lame. What it did quite well was clean and semi-clean tones. It also could do crunch tones but not that well.

I have changed the preamp to this: https://www.youtube.com/watch?v=qumL2poI7dQ (except for the tone stack where I kept the 33k/500pf treble, 22nf bass and mid) and I like it better for any tone.

Cheers Stephan

[bluezinger]

I have a McIntyre Bluesmaker II PL 40 amp head that John custom made for me back in 1995. I used it for my main studio amp for years. Haven't used it in a long time. Anyone have any idea what it might be worth? It's pretty beat cosmetically but is in fine working order and sounds great. I also own a Silverface Bandmaster that he modded which sounds pretty cool. Thanks! Chris