Weber 6M45P Head Kit Build

[miallen]

Where is a good place to post build questions?

I just bought (ordered) a weber 6M45P head kit which is a JMP 50 clone.

Schematic and layout here:

https://taweber.powweb.com/store/kits_60b.htm#6M45PH

I have a lot of experience designing and building circuits. Not so much guitar amps but I know how to make a circuit quiet and I suspect that's probably one of the most important if not THE most important skills when building high gain amp that throws a lot of current around.

This kit seems like a real bargain. It sure is cheap. I could buy fancy-pants OT and it would still be cheaper than the next kit. But I see a lot of room for improvement in this kit. For one the filter cap situation is almost hilarious. There are 12 (yes, twelve) filter caps that could be reduced to 3 parts for probably $20. I know no one can see inside but I'll know what it looks like in there.

So what sort of tweaks and upgrades would you do on this kit? A nicer turret board? Different OT? Post PI master volume? Granger high-voltage effects loop?

There must be people that have cobbled together a half-dozen of these kits over the years. Where do they hang?

 

[Guitar-Rocker]

While a builder, but not a kit builder, I took a peek at the Weber kit your link indicated. I personally don't care for the Weber layout shown, with V1B's cathode resister/cap next to the PI but for a first build it might work out ok. If it were I building, I'd follow Marshall's filter cap scheme rather than Webers. I cannot attest to Webers components in kits, but I did buy and build off of one of their chassis once (combo chassis only). It was an ok chassis.

As far as Weber iron. I sold one of my amp builds locally to Brian, who a couple of years later loaned it out for a short period. When it came back he asked me to look it over as it now sounded terrible. I found the guy Brian loaned it to had replaced the OT with a Weber OT, why the swap.... I never heard the reason behind that. I sourced one of my OT's, replaced the new Weber, and the tone was back again. It was a $100 learning curve for Brian about loaning out amps.

 

[Vostre Roy]

Hey man, cool to see another one going for a Weber build

I've built two Weber amps (8CM100 and 6M45P) so far and worked on a 3rd one (Halle) who belongs to a friend. If you are looking to improve parts, I'd suggest to look for better trannys and pots. Stock transformers works fine and gives a decent sound, but we swapped the OT in the Halle for an Hammond and it really improved the sound, so I'd guess that an Heyboer or Mercury Magnetic would be an improvement too. I really hate the pots supplied though, feels like chinese cheap crap, we also changed all the pots in the Halle and it was a huge improvement, probably better than the OT swap. I'm looking to do the same for my 8CM100.

That being said, here's my 6M45P completed build thread with the schematic I've used (added a 1987/2203 switch and PPIMV): http://www.marshallforum.com/workbench/78097-weber-6m45p-completed-build.html

I have used the filter cap layout from Weber, used a dual gang 1Meg pot for both channel's input gain control and ditched the impedance switch. Beside that, its pretty much stock.

Cheers man, feel free to ask any question, I ain't an expert builder but my stuff worked so far ahaha

 

[gldtp99]

I got an abandoned Weber 6M45P head from ebay----- It was a kit that someone tried to build but gave up on-------I used a new 2204 type turretboard, new pots, etc and made a slightly modded 2204 out of it.
I'm not satisfied with the overall tone---- I believe it is the Weber OT that is the problem---- I've built many 2204 circuits and have checked this one over.
The amp operates fine---- it just doesn't sound right--- It's not bad, really, just not good enough----- when I get time, I might swap OT's with a ClassicTone 2204 OT I have on hand.
Overall the Weber kit seems to made with cheap parts---- I'm not one who thinks that throwing money at a build (in parts cost) necessarily makes a better amp but there is a limit to cutting corners on component cost---- I won't be buying any Weber kits after rescuing this kit build attempt.
I've used Weber brand (Chinese) PT's in several different amp builds over the yrs and all have performed well----- But I'm not a fan of the OT in this Marshall-ish kit.
But I've got many amp projects to do and little time to spend on them----- so this Weber kit OT upgrade will have to wait................... gldtp99

PS---- the Vintage Orange OR80 circuit build I did in this vid uses a Weber Chinese PT (a Twin Reverb type PT)----- this band, Dead Oak, has been using this amp for several years with no problem at all:

https://www.youtube.com/watch?v=xzb04NnZ46o

This amp has an Edcor 100 watt, 4.2k primary, 4/8/16 ohm secondary OT

https://www.edcorusa.com/cxpp100-ms-4_2k

 

[RussBert]

Sorry to hear you already ordered it.


I bought & built a 6M45 kit several years back. I learned a lot, but eventually replaced almost all the components. What weber has in the kits can be considered the cheapest junk available. When I was done, I had more money in it than if I had bought a Metropolous kit (which are sadly no longer available).

Mojotone and Triode offer much better kits for a fair price

 

[miallen]

Where is a good place to post build questions?

I just bought (ordered) a weber 6M45P head kit which is a JMP 50 clone.

Schematic and layout here:

https://taweber.powweb.com/store/kits_60b.htm#6M45PH

I have a lot of experience designing and building circuits. Not so much guitar amps but I know how to make a circuit quiet and I suspect that's probably one of the most important if not THE most important skills when building high gain amp that throws a lot of current around.

This kit seems like a real bargain. It sure is cheap. I could buy fancy-pants OT and it would still be cheaper than the next kit. But I see a lot of room for improvement in this kit. For one the filter cap situation is almost hilarious. There are 12 (yes, twelve) filter caps that could be reduced to 3 parts for probably $20. I know no one can see inside but I'll know what it looks like in there.

So what sort of tweaks and upgrades would you do on this kit? A nicer turret board? Different OT? Post PI master volume? Granger high-voltage effects loop?

There must be people that have cobbled together a half-dozen of these kits over the years. Where do they hang?

Here are some pics. Seems to work fine so far but I've only been playing for a few hours so I'm not absolutely certain that it's functioning exactly as intended. I am getting some strange frequency responses under the analyzer (notches at 200Hz in some settings - not sure if that sort of thing is supposed to happen). At some point I got some squealing using the send on the Granger send / return.

Started with switched input (see http://el34world.com/Forum/index.php?topic=18700.msg192454#msg192454 for details regarding input switching scheme) and master vol:

Shielded cables where appropriate:

Used daughter board for original 1987 tube bias instead of separate PT tap.

Granger Ultimate FX Loop. Unfortunate even though it only draws ~1.5 mA of course this causes a 30V drop in the supply at the PI and downstream. Might try higher voltage tap of PT to compensate.

Changed the layout a little bit.

Spread the power supply caps out with their own grounds running back to star which on the lower-left corner bolt of the OT.

Done.

More done.

See bias pot in between power tubes.

Closeup of input switching and PPIMV.

Nice kit but as you can see it's far from the stock parts. But most of the Weber parts are actually quite good. The cab and chassis are really nice. The eyelet board worked out fine. I used their pots (although the 5K presence control feels a little loose). I went for the ClassicTone OT. I didn't use their thin cloth wire but honestly I don't think it would have made much if any tonal difference. As you can see I elected not to use the bundle of caps the Weber layout calls for. It sags ~50 volts when cranked but it sounds good to me. Only thing I'm worried about is the FX loop. I think I might have to yank it if I can't get the voltage up (fortunately I used the 125V primary and lower secondary so I might be able to bring things up).

 

[RussBert]

Your 1 ohm resistors are not installed properly. The lead should go through both the #1 and #8 terminal, then the resistor body, then to ground. You measure the current draw between the resistor body and the pins.

The (1k?) screen resistors look woefully small. You want 5 watt resistors here. I don't see screen grid resistors either. Perhaps they're on the board? I put them right on the socket on pin 5.


Here's a JCM 800 2204 as an example

 

[SirArcsAlot]

Also FWIW, the right hand rule was not followed here. All the trannies should be at 90 degree angles of each other and the OT and choke are both parallel.

 

[miallen]

Your 1 ohm resistors are not installed properly. The lead should go through both the #1 and #8 terminal, then the resistor body, then to ground. You measure the current draw between the resistor body and the pins.

The (1k?) screen resistors look woefully small. You want 5 watt resistors here. I don't see screen grid resistors either. Perhaps they're on the board? I put them right on the socket on pin 5.

I find it difficult to believe that holding the suppressor screen at ground as opposed to through a 1R to ground is going to make a shred of difference. The voltages generated across it are going to be really small in the scope of things. In a cathode biased amp it might be important but not with a 1R resistor. And this way you don't need extra little terminal strips.

The screen resistors are 470R 1W so screen current would have to be like 20mA before they even got warm. Maybe a 1K would need to be more because of the larger voltage drop but I think 1W is fine for 470R. I just used what came with the kit so for now I'm going to assume they're ok.

Also, I have to wonder if maybe deliberately making the screen resistors a sacrificial part is actually not a bad idea. Meaning if the tube shorts, the screen resistor will blow out and protect more expensive parts like the transformers (but this is just thinking out loud - I could be wr-wr-wrong).

The input grid resistors are soldered directly to the grids. You just can't see them in the pics. Actually you can see one of them in the upper right corner of the second pic.

Regarding the right-hand rule about transformers, it seems to me their fields are not correlated. The PT is laying down and the OT is upright so I don't think there is any orientation where the fields could be aligned. As for the choke I think it's probably far enough away to not be a problem. I just used the holes already in the chassis.

 

[neikeel]

I find it difficult to believe that holding the suppressor screen at ground as opposed to through a 1R to ground is going to make a shred of difference. The voltages generated across it are going to be really small in the scope of things. In a cathode biased amp it might be important but not with a 1R resistor. And this way you don't need extra little terminal strips.

Correct, makes no difference (although I do it same way as RussBert myself)

The screen resistors are 470R 1W so screen current would have to be like 20mA before they even got warm. Maybe a 1K would need to be more because of the larger voltage drop but I think 1W is fine for 470R. I just used what came with the kit so for now I'm going to assume they're ok.

Also, I have to wonder if maybe deliberately making the screen resistors a sacrificial part is actually not a bad idea. Meaning if the tube shorts, the screen resistor will blow out and protect more expensive parts like the transformers (but this is just thinking out loud - I could be wr-wr-wrong).

If you want a robust gigging amp go for 5w as yes 1w will be sacrificial if a tube pops, but then so will the 1R 1/3w bias resistors.

The input grid resistors are soldered directly to the grids. You just can see them in the pics. Actually you can see one of them in the upper right corner of the second pic.

Regarding the right-hand rule about transformers, it seems to me their fields are not correlated. The PT is laying down and the OT is upright so I don't think there is any orientation where the fields could be aligned. As for the choke I think it's probably far enough away to not be a problem. I just used the holes already in the chassis.

The choke is an example of why I am not convinced that the Weber kits are ideal. There are examples of poor component positioning which will result in cross talk and PO as the gain levels go up, it is good practice to keep the plate wires low to the chassis and grid wires as far away as possible, don't bundle signal wires together if you can't avoid it, move all the control wires off the pots and run them separately to the pots.
Regarding the loop you normally set the amp up first without it to get your preamp tube voltages where you want them, then install the loop with a dedicated dropper to get its operating voltage correct, but decrease one of the droppers between the screens and PI from, lets say 8k2 down to 4k7 that will help restore the preamp voltages (assuming you are picking up your loop voltage post PI supply?)

 

[miallen]

If you want a robust gigging amp go for 5w as yes 1w will be sacrificial if a tube pops, but then so will the 1R 1/3w bias resistors.

The choke is an example of why I am not convinced that the Weber kits are ideal. There are examples of poor component positioning which will result in cross talk and PO as the gain levels go up, it is good practice to keep the plate wires low to the chassis and grid wires as far away as possible, don't bundle signal wires together if you can't avoid it, move all the control wires off the pots and run them separately to the pots.
Regarding the loop you normally set the amp up first without it to get your preamp tube voltages where you want them, then install the loop with a dedicated dropper to get its operating voltage correct, but decrease one of the droppers between the screens and PI from, lets say 8k2 down to 4k7 that will help restore the preamp voltages (assuming you are picking up your loop voltage post PI supply?)

The bias resistors are 2W. They are exceptionally small but I bought them from Mouser myself.

Weber kits are definitely not "ideal". But they are cheap. And the amp rocks. I have been noodling on if for 2 days now and there are multiple sweet tones that can be dialed up. The threshold between being clean and distorted is exactly what I had hoped for.

I happened to take a pic of the high current business before sowing it up.

As you can see the grid wires are actually flat on the chassis and the OT wires are draped above. I left some extra secondary wire for no reason and I somewhat regret that now. And the grid cable didn't need to cross over twice. But it would all be hard to get to now.

This pic shows the HT supply wires which are white.

The fat white wire twisted around the OT secondary wires is the A supply coming in. The white wire from the left is the choke and the fat white wire going down is the OT primary center tap. They're only connected to the board as something to solder to.

I have not had any oscillation problems at all playing through a regular load. But the Granger FX loop did cause oscillation using the send with the mid and trebles above a certain point.

What are ideal voltages anyway? Last I checked I had:

A 434
B 432
C 254
D 218
E 205

I actually thought about using a separate dropper resistor for the Granger loop. I will definitely have to do what you describe. Right now I'm connecting to C (the PI supply). The PI dropper resistor is actually 22K. You can see it in the second pic. It's actually under the eyelet board so I'm not sure I want to fiddle with that.

I also used the lower voltage PT secondary which is only 660VAC vs 720VAC. So the 720VAC tap should give me just under 500VDC. However I used the lower voltage because I noticed the Weber PT is physically smaller and weighs noticeably less than the ClassicTone PT for a JMP50 and so I though it might be better to use the lower voltage secondary. I also used the 125VAC primary as opposed to the 120VAC so that's another way to boost voltage.