ab165 bassman with EL34's

drew_half_empty

drew_half_empty

Looking for Real Life
anyone ever tried this? seems like (with a few additions like a mid knob, presence knob, and a blend pot to act as a gain control) it'd be one hell of a rock amp

I'm considering building one, that's why. I like the mid complexity of EL's but feel they lack lows & highs, and an ab165 bassman is pretty much all lows & highs, so this seems like it'd be a great match as far as getting the best of both worlds
 
Re: ab165 bassman with EL34's

I have experimented along these lines with good results. Before expaining what must be done, let me caution you that if you havn't much experiance in such matters find someone who does. You don't want to get Zapped!

EL34's have three grids, were 6L6's have two. Pin 1 services the extra grid on EL34 amps. On a Fender you need to solder a conection from pin 1 to pin 8 (cathode) externally, and disconnect the 1500 ohm resistor and the wires that connect to pin 1. Usually this resistor is soldered to pin 1 and 5 on an old Fender. It and the wires need to still connect to pin 5. The 470 ohm resistor that is connected from pin 4 to pin 6 needs to be changed to a big (5 watt) 1000 ohm resistor.

Next you need to modify the bias circut. IIRC, the AB165 doesn't have true bias adjustment. It's a useless "hum balance" thing that just changes the bias voltage slightly in case there's a hum from one set of 6L6's to the next. This circut has additinal resistors and wires. You need to change it so it's like a 50 watt Marshall plexi bias supply, or more like the AA864 bias Black face circut. You may have to additionally adjust the value of the resistor in series with the bias diode to have the proper voltage range needed to bias EL34's.

Once you do all this you can then run either EL34's or 6L6's with a proper rebias.
 
Re: ab165 bassman with EL34's

Guitar Player had an article several years ago which was a conversion of a BF Bassman to EL34s, and added gain - the point was to get it more in Marshall territory.

So, it's not a really far fetched idea. However, my feeling is that you should do this on a good candidate for modding, and not a stock BF. Most BF and early SF Bassmans really need very little modding to sound killer.

I think the best mods are converting the bias to a "real" bias, and voicing the bass channel for a guitar. These two mods can be done fairly easily by a good tech.
 
Re: ab165 bassman with EL34's

drew_half_empty said:
anyone ever tried this? seems like (with a few additions like a mid knob, presence knob, and a blend pot to act as a gain control) it'd be one hell of a rock amp

I'm considering building one, that's why. I like the mid complexity of EL's but feel they lack lows & highs, and an ab165 bassman is pretty much all lows & highs, so this seems like it'd be a great match as far as getting the best of both worlds
Click to expand...

If you're going to BUILD all this from the ground up (as in getting out the soldering guns) then kudos and hope it turns out well.

If you say build as in "buy an amp and mod it to the point where it's not the original amp anymore", then it's probably best to go get an amp thats as close as possible to what you'd want in the end result, and only mod if you have to.

On a side note I think an amp lacking in certain frequencies has more to do than the AMP than with the tubes it's running. All-tube amps, ironically, are not just all tubes. ;) There's the preamp and power amp controls and what their frequencies are centered at. There's the grade of the power transformers. Even whether the chassis is ferrous or not will have some effect on the sound... lots of little changes make big changes. As for me I have no trouble getting a really nice, even, balanced tone thats rich in all frequencies from my amp, which currently uses EL34s. I can flip a switch and move to 6L6's or 5881s if I want to. It's still going to sound like my amp but with a slightly different flavor.

Tried a good old Marshall 2203 yet? ;)
 
Re: ab165 bassman with EL34's

chopstherocker said:
By the way, what's with the 170W Bassman 100? That sounds stupidly loud. For a bass amp, maybe, for a guitar amp...can you say OVERKILL!!!!!!!!!!!!!!?

Go the AC/DC route. 100W JMP. No effects, all on 10. Could kill small cats with that volume.

There is no such thing as the best of both worlds kiddo. I was your age once and thought dumb things too. You want a loud amp. Go Marshall tube 50W, You want stupidly loud, go Marshall JCM800 with Drake transformers, the settings are OFF/BLEEDING EAR DRUMS.

Don't mess with a perfectly good POS 70's Bassman in the first place.
Click to expand...


god i hate it when new people come on here & screw with me like this. You missed countless discussions on this topic, and i'm not about to go into it again.

and it sounds really, really friggin good, especially with a tube screamer, so don't insult things you know nothing about.

and my transformer is bigger than a drake transformer, so there



ANYWAYS, no man i haven't tried out a 2203 yet, well, actually i can't really remember what that is. I've tried a jcm2000, which sounded kinda cheap to my ears (probably due to some cheap components), aaand a jumped plexi reissue with a new mercury magnetics transformer, which sounded pretty good, aaand an early jcm900 which wasn't bad, but that's about it

and no, i was talking about building it from the ground up, a few of my friends are starting to build amps & getting awesome results for $500-600, so i figure hey, why not give it a whirl? IMO the ab165 doesn't need any more gain, all on 10 it's pushing the 'too much gain' boundary
 
Re: ab165 bassman with EL34's

I've played the tweed RI & loved it, but it's not the tone i'm going for with this build, nowhere near warm enough. I would like to own one at some point though

and my gripe with marshall is the cheap components & high prices. The stock transformers (on the new ones) are total junk.

but i would also like to own a jmp and a jtm45 at some point

but once again, neither are what i'm really going for, even though the JMP comes real close

basically what I'm doing is taking the jtm concept (brit-ified bassman) and jumping it foward 20+ years

IMO the jtm really was the best of both worlds, for its time

then again the other side didn't really exist?
 
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Re: ab165 bassman with EL34's

if you cant handle it yourself and you got the cash, perhaps you could find a builder to help you on this one.

I like the tone that you're looking for-like a JTM45, but instead of being based on tweed, you want it based on the more 'powerful' and tighter BF circuit.

What do you mean by not warm enough? Not dark sounding enough?
 
Re: ab165 bassman with EL34's

Have Scott_F make you an Edana (JTM45 or Plexi). :fing2: I have one, it actually is the best of both worlds, Fender clean and classic Marshall overdrive. Loud as hell btw.
 
Re: ab165 bassman with EL34's

Scott_F said:
Wait till you end up picking up a 4x12. You think it's loud now? :) Haha!
Click to expand...

I DO have a 4x12 right now haha... although I may be reconsidering... ehh forget that. *MUST HAVE MOJO 4x12*
 
Re: ab165 bassman with EL34's

Well, if you have a 4x12, why do you need/want another one? If it sounds good, keep it! Save your cash!
 
Re: ab165 bassman with EL34's

Scott_F said:
Well, if you have a 4x12, why do you need/want another one? If it sounds good, keep it! Save your cash!
Click to expand...

Because its an MG cab made of particleboard with questionable speakers... I guess Its hard to make the Edana sound BAD, but I've been told Celestions would be a major improvement.
 
Re: ab165 bassman with EL34's

drew_half_empty said:
well, how would you describe the tone of the finnished amp?
Click to expand...
Hmm.. a little smoother and noticably louder, with a bit more "Marshall" when it started clipping. In both cases it started distorting on about 4 1/2-5. It didn't really add a bunch of missing mids. The tone stack on a BF or a SF is pre-set to like 4.

*On these amps the caps between the preamp triodes cathode and ground go bad with age and cause noises and crackles. Go to BF specs, or simply replacing the the caps and the resistors with plexi Marshall values caps will noticably make it sound more Marshall "flutey" like.

*If you get someone good to convert it to EL34's, then you can switch back to 6L6 and back to EL34 without much problem, and without screwing the basic amp up. This isn't that major of a mod to the basic design and it's certianly reversable.

The suggestion to have the bias supply set up right, may be your best couse of action, as you will be suprized how much you can fine tune the amp (including mids) with a real bias set up.

I'd have the amp set up to BF specs with adjustable bias for sure.
 
Re: ab165 bassman with EL34's

Quencho092 said:
if you cant handle it yourself and you got the cash, perhaps you could find a builder to help you on this one.

I like the tone that you're looking for-like a JTM45, but instead of being based on tweed, you want it based on the more 'powerful' and tighter BF circuit.

What do you mean by not warm enough? Not dark sounding enough?
Click to expand...

i dunno if dark is really the right term.

ok, think about a mesa dual rectifier, v30 loaded, and a jmp with g12h30's

the rectifier has that real buzzy kinda high gain tone, when you kick on the distortion it's REALLY friggin obvious

now think about the JMP, it's really, really smooth sounding, you get just a tiny bit of pick attack, some compression, sustain, and warmth when you crank it. All your bends & stuff become bluesy as all hell, but you got solid chording.

the jmp is obviously a lot closer to what i'm going for, it's not really dark, by my standards, but it's real thick & smooth


as far as the mid thing goes, yeah i'm definately gonna hafta add the mid knob for that reason, and maybe even toy with different resistor values, maybe a JMP resistor value on the mids

again the overall point is to get noticeable, EL-type mids without losing the bottom or top end that that circuit of bassman is known for, and also warm it up a bit. I think the conversion itself, with, oh, lets say JJ el's & EH preamp tubes, if not electro harmonix all around, should do it

of course i'll also hafta find the right combination of speakers to bring out all the right frequencies & voice them right
 
Re: ab165 bassman with EL34's

Curly said:
Guitar Player had an article several years ago which was a conversion of a BF Bassman to EL34s, and added gain - the point was to get it more in Marshall territory.

So, it's not a really far fetched idea. However, my feeling is that you should do this on a good candidate for modding, and not a stock BF. Most BF and early SF Bassmans really need very little modding to sound killer.

I think the best mods are converting the bias to a "real" bias, and voicing the bass channel for a guitar. These two mods can be done fairly easily by a good tech.
Click to expand...


I have an AB165 bassman modded as specified to use EL-34.

FOR SALE $550 firm
 
Re: ab165 bassman with EL34's

B2D said:
Than why don't you just BUY one instead of mutilating a Bassman, for chrissakes.

Additionally... https://forum.seymourduncan.com/showthread.php?t=47947&highlight=apple

I'm done with this runaround.
Click to expand...


hah it's closer, but not what i'm picturing. JMP just kinda ballparks it

i'm taking 2 things that are associated with the tone in my head & combining them, in a totally new amp, not mutilating something that will rise in value

on that note, the one that's been done is tempting, REALLY tempting.

shoot me a PM with more info (what kinda tubes, last retube, what all was changed, quirks (if any) & lemme see how much money i have after the holidays
 
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