Plausibility of putting a JTM45 circuit in my 5E8A?

[BobL]

So... Bassman and JTM45 are so similar, I was wondering about replacing the 5E8A (which I'm just not happy with) with the JTM45, and installing it in the same chassis, running 6L6GCs (same transformer I've currently got, yeah?), and playing it through my Weber P12Qs...  I think it might sound pretty good (and closer to what I want, being able to get a little dirtier, having something a bit less loose).

It seems like mostly this should work... I'd have an empty preamp tube socket hole, but I could use one of the octal's for one of the big 450v can filter caps... not sure where I'd put the other one.

Anyone have thoughts?  Anyone done something along these lines?

[sluckey]

I think it's very doable. I would probably put both cap cans in the holes where the two 5U4s are. Then enlarge the hole that currently has the PI tube such that you could put one of the 6L6s there. That leaves three little tubes and no extra holes. Kinda like this pic. Just imagine the three tubes on the right are octals.

[BobL]

Oh, now that's thinkin'!

[Willabe]

There was a thread not long ago on a 5E6A/5E8A. I forget if you posted in that thread.   

Not to discourage you on reworking your amp but;

1. Have you tried running it with only 1 rectifier tube?

2. Have you tried taking out the NFB loop that's around the tone stack driver/cathode follower?

3. Have you tried a 12AX7 (or 5751) for the input preamp tube and/or for the tone stack driver/K follower?

4. You can also bridge the 2 input channels with a short jumper (just like on a 4 input Marshall) and get a little more drive by turning up both channels.   

If you haven't tried these yet you might want to before you tear/cut up the amp?

Any 1 of these or a combination of these might go a long way in helping you get closer to what you want.


             Brad       

[BobL]

There was a thread not long ago on a 5E6A/5E8A. I forget if you posted in that thread.   

Not to discourage you on reworking your amp but;

1. Have you tried running it with only 1 rectifier tube?

Yes.  I do prefer 1.

2. Have you tried taking out the NFB loop that's around the tone stack driver/cathode follower?

No... I'm not quite conversant enough to know what this means....

3. Have you tried a 12AX7 (or 5751) for the input preamp tube and/or for the tone stack driver/K follower?

Yes, and I currently have some NOS 12AT7s in there that I thought were the best sounding match for the amp.

4. You can also bridge the 2 input channels with a short jumper (just like on a 4 input Marshall) and get a little more drive by turning up both channels.   

Yeah... *more* gain isn't quite what I'm after, just a better flavor of it, perhaps... if that makes sense.  It's pretty loose and farty on the low end, and overly bright on the top...  I get a little bit of non musical distortion when I start to turn it up, which may be an issue somewhere, but everything is testing out ok, and I'm not sure it is caused by a build issue.

If you haven't tried these yet you might want to before you tear/cut up the amp?

Any 1 of these or a combination of these might go a long way in helping you get closer to what you want.


             Brad       

Appreciate the reply... I've been trying a lot, and I haven't quite given up yet, but... I wonder if something more in between Bassman and JTM would fit the bill... dunno.

[Willabe]

Ok, your title says 5E8A (tweed twin) then you wrote Bassmen. Which is it? There is a tweed bassmen 5E6A that's very close but not exactly the same.

(and closer to what I want, being able to get a little dirtier, having something a bit less loose).

Yeah... *more* gain isn't quite what I'm after, just a better flavor of it, perhaps... if that makes sense.  It's pretty loose and farty on the low end, and overly bright on the top...  I get a little bit of non musical distortion when I start to turn it up,

Tweed amps are said to be smoother/warmer than a Marshall so I don't get the overly bright on the top. I'm not saying your wrong but that seems a little odd.

A lot of guys here say the webers need to be well broken in to knock the high end edge off. I don't have any knowledge of which weber model is what sounding wise.

What guitar are you playing? What PUP's are in it? Do you play the lead PUP mostly? Any stomp boxes up front?

A lot of guys change the cathode bypass caps to a smaller value to tighten up the bass end, say 10uF and lower.

One of the 2 channels is a bright channel with a treble bypass cap wired across the volume pot, have you tried the normal channel?


             
                Brad     

[Willabe]

The tone stack negative feed back loop is in blue and the cathode (K) bypass caps are in red.


              Brad       

[BobL]

Ok, your title says 5E8A (tweed twin) then you wrote Bassmen. Which is it? There is a tweed bassmen 5E6A that's very close but not exactly the same.

I was referring more to how modifying this amp with a JTM circuit would end up being fairly similar to a Bassman - the amp is currently a 5E8A.

Tweed amps are said to be smoother/warmer than a Marshall so I don't get the overly bright on the top. I'm not saying your wrong but that seems a little odd.

This was entirely what I thought I'd be getting when I built this, but it sure isn't warm or smooth to me.  This is why I can't rule out that I've gotten something wrong, or a bad component, or something... but I haven't been able to find anything so far.
[/quote]

A lot of guys here say the webers need to be well broken in to knock the high end edge off. I don't have any knowledge of which weber model is what sounding wise.

I don't actually have the Weber's yet - they will be here Tuesday.  The current speakers are ceramic P12Qs, so absolutely step one is to see how things sound with the webers... it might be that these Jensens are just total crap.

What guitar are you playing? What PUP's are in it? Do you play the lead PUP mostly? Any stomp boxes up front?

I have a Gibson Custom '58 Reissue with a Wolfetone Dr. Vintage humbucker set, and a tele custom with the same humbucker pickup in the bridge and a Fralin in the neck.  Through my AC30 the tele is warm and clear.

I have a rangemaster based germanium boost/fuzz (Creepy Fingers Sugarboost) that seriously sounds amazing through any amp I've ever plugged it into (AC30, JCM800, JTM45, Fender Blues Jr), and it sounds like complete dog crap through the 5E8A.  Has me scratching my head.

A lot of guys change the cathode bypass caps to a smaller value to tighten up the bass end, say 10uF and lower.

Yeah, I actually did this on the last JTM45 I built, and liked the result.  Have not tried it here yet.

One of the 2 channels is a bright channel with a treble bypass cap wired across the volume pot, have you tried the normal channel?

Yeah, I've mostly worked with the normal channel, but have extensively tried both.  I've given the amp over a month to try and see if I just needed to figure it out, etc., and it's just not working well for me at all.

[HotBluePlates]

Tweed amps are said to be smoother/warmer than a Marshall so I don't get the overly bright on the top. I'm not saying your wrong but that seems a little odd.

This was entirely what I thought I'd be getting when I built this, but it sure isn't warm or smooth to me.  This is why I can't rule out that I've gotten something wrong, or a bad component, or something... but I haven't been able to find anything so far.

To me, the later, bigger tweed amps have a different EQ curve but are otherwise a lot like the 60's Fender amps.

In other words, a 5F6-A Bassman circuit will be brighter than you think, and have an EQ curve like a 60's Fender rather than like a tweed Champ.

I've owned a '54 Princeton and a '55 Tremolux and built copy 5E3 Deluxes, 5F4 Supers and 5F6-A Bassman amps. The 5F6-A and Super have different, but brighter, voices than the smaller amps.

Speaker can and do make a huge difference in the final sound, though.

[HotBluePlates]

... on the last JTM45 I built ...

You can probably ignore my comments then, as you already know what this circuit sounds like.

...  Through my AC30 the tele is warm and clear. ...

But maybe you already understand what I said about amps sounding other than what you imagined they'd sound like. You already know that everyone talks about "AC-30 chime" but if you play clean without boosting treble an AC-30 can be downright dark-sounding.

Actually, finding out myself how most of the vintage amps sounded alike clean lead me away from collecting vintage amps and into building my own. I was quite surprised how most amps sounded good but didn't live up to the imagined, hyped sound I thought I'd get when I bought them.

Sorry for the detour...

[BobL]

Oh, detours are definitely good stuff!

My thinking is that I'm not happy with where I am, and I do like the sound of 60s Fenders and Bassman amps, and I really am missing having a mid control, so if speakers don't magically fix everything, then this might be something to try since I have an amp I'm not using with its current sound.

[BobL]

So I've had the Webers in there for a few days, and they are clearly a much better sounding speaker.

I also swapped the PI coupling caps for .47uf and replaced the LarMar MV I'd built into it with a straight up 'Rich' PPIMV, and I think all that helped... but it still isn't there.

The mids seem very scooped, and with no mid control and the bass/treble needing to be at at least 6/12 to get any volume out of the amp, it's hard to bring them in, so that's a frustration... maybe the PI cap change contributes to this?  The low end seems tighter.

I also have a static/crackle that comes in when I start to overdrive the amp - like there is the normal overdriven sound which is musical and decent, and then this crackle in the background - the harder I play, the more static I get.  This was present with both MV setups, though *possibly* more pronounced with the LarMar.

Could this be a bad electrolytic cap?  Later today I hope to take a pencil eraser and tap my way through the amp to see if I can get bursts of static from anything.  I feel like until I figure that part out, I'm probably not really hearing the amp or giving it a fair shake.

I also realized that the other issue to figure out if I put a Bassman/JTM circuit in here would be, with my MV, needing one more control hole... I guess I could put the extra control in the first bright input, and delete the 'low' input on the bright channel.

[BobL]

Ok, so I started tapping through the amp, and the one place I was getting some noise is on V2 when I tapped the tube itself - this is a vintage mullard 12AT7.

I put in a modern JJ ECC83S, and got a pretty loud hum, and microphonic sound when I tapped the wire leading to pin 7 of V2.

I put in another modern JJ ECC83S, and wasn't getting the hum, but if I tap/move that wire going to pin 7 (or move the pin itself), I get pops and crackles...

I took a probe and bent that pin socket together, and that fixed that problem.

I still have the static/distortion thing going on when overdriving... hrm...

[BobL]

Aaaand... it's totally the MV.  If I dime the master, it pretty much goes away.

Crap.  Is there really not an effective MV to put in this amp? Do I just need to go stock and use an attenuator or something?