Planning for a new build.

[Alan0354]

Hi guys

I just button up my amp and sit on it for a little while. I want to plan on a future build. The last one is more a Fender style sound. I am starting to plan on the next build. I am considering a Marshall type this time. I have a Marshall JCM900 Dual Reverb combo that is not up to par at all, so that will be my next logical platform to build my next amp. I think I want to rip out even the power amp even though it's a marshall. The pcb is a single layer board with no plated through holes, I don't trust the board.

1) Is the OT the most important part of Marshall sound?
2) Is it important to use EL34 instead of 6L6 or 6V6? I don't need high power. 30W would be ideal.
3) Should I get a 50W Marshall OT instead of using the existing 100W OT in the Dual Reverb? I am happy with the OT from Classic Tone, should I get Classic Tone OT designed for Marshall?
4) Can I get away with using the PT, it's a 100W PT, can I just put a say 150ohm resistor in series to create some sag to fake a smaller PT?
5) The cabinet of the Dual Reverb is quite thin, when I play through the cabinet, I feel there is boxy sound. Do you think I can reenforce the cabinet to make it better? I really like the size, the looks and the two handle for easy carry, but it really sounds bad.

Please give me some guidance.

Thanks

[jazbo8]

Since you do not like your JCM900 and you want less power, it does not seem worthwhile to modify it - it would be better for you to sell it as is to another musician who can appreciate/use it. As for the order of importance of the various parts in an amplifier, imo, it goes like this:

1) speaker;
2) cabinet;
3) OPT;
4) PT;
5) circuit topology;
6) layout & construction;
7) tubes;
8) passive components.

YMMV.

[Alan0354]

Since you do not like your JCM900 and you want less power, it does not seem worthwhile to modify it - it would be better for you to sell it as is to another musician who can appreciate/use it. As for the order of importance of the various parts in an amplifier, imo, it goes like this:

1) speaker;
2) cabinet;
3) OPT;
4) PT;
5) circuit topology;
6) layout & construction;
7) tubes;
8) passive components.

YMMV.

Thanks for the suggestion. If I sell this, I still have to buy another amp. The Marshall does not worth much, this is not like the JCM800 all tube. It is solid state front end with tube power amp. I checked on ebay, it's some where like $500 to $600. The Marshall chassis is very nice and thick, it is of high quality. So I am not gaining much selling and then buy another one. Not to mention I don't like people coming over and test the amp and all.

1) I am planning to either use the Celestion G12T-75 or buy another one less of American sound. Some people suggested WGS ET65.

2) Well, the cabinet will be the Marshall small combo.

3) You think the Classic Tone Marshall OT is going to sound very different from my Classic Tone Vibrolux/Bandmaster OT?

7) So you think there is not much difference between EL34 and 6L6 or 6V6?

8) Ha ha, I make it a strong point to get the cheapest components. I use all MF resistors, ceramic cap if possible, for tone caps, I use the cheap Weber caps!!!! I don't believe these make a dent of a difference. I use these in my amp and I am happy.

[jazbo8]

Still think it's better to sell it and use the money to buy good OPT, PT may be even a speaker (which you are going to do anyway) for the new build. Classic Tone makes great transformers, I doubt one would sound much different from the other, since the same manufacturing process is used. There is a difference between EL34 and 6L6/6V6 - it is one of the key factors to have a British vs. American sound - that's no myth. Electrically, EL34 is a pentode while the 6L6/6V6 is a beam tetrode, so they do have different characteristics. If you use adjustable bias, then you can swap them for different tonal preferences.

[J M Fahey]

I have a Marshall JCM900 Dual Reverb combo ..... The pcb is a single layer board with no plated through holes, I don't trust the board.

I bet Marshall will be very worried about that.

1) Is the OT the most important part of Marshall sound?
2) Is it important to use EL34 instead of 6L6 or 6V6? I don't need high power. 30W would be ideal.
3) Should I get a 50W Marshall OT instead of using the existing 100W OT in the Dual Reverb? I am happy with the OT from Classic Tone, should I get Classic Tone OT designed for Marshall?
4) Can I get away with using the PT, it's a 100W PT, can I just put a say 150ohm resistor in series to create some sag to fake a smaller PT?
5) The cabinet of the Dual Reverb is quite thin, when I play through the cabinet, I feel there is boxy sound. Do you think I can reenforce the cabinet to make it better? I really like the size, the looks and the two handle for easy carry, but it really sounds bad.

1) no
2) yes
3) yes.
Do it right from the beginning ; misusing OT by mismatching taps, loading tubes with inductance (both series and parallel) wildly different from original and then expecting original sound is silly.
4) [facepalm]
5)

The cabinet of the Dual Reverb is quite thin ..... it really sounds bad.

Want real Marshall sound? get a 4x12" and load it with Celestions/"British" Eminence/Scumback/"British" Weber/WGS

Or at least a relatively large *closed back* 2 x 12" and put JCM900 combo speakers there.
Similar to

or

or

[Alan0354]

What do you think of this PT for the Marshall build? https://taweber.powweb.com/store/022798intsch.jpg.

This is again a Weber PT. Very much the same as the Deluxe PT, just this one has 720VAC CT @200mA. This is good for about 40W to 45W using a pair of EL34. The reason I choose this over the Classic Tone Marshall 50W PT or even the Weber for Marshall is mainly because this one has 5V@3A winding. This is very important as I rectifier this to get 6VDC for all the relay, the positive rail for the HV opamp for power scaling and for the mute circuit. All the Marshall PT does not have this winding.

Yes, I might get unbalanced one again, but hey, I think I came out on top on the last one!!!! This one is a lot cheaper than the Marshall type PT.

Another thing is, the -45V tap of the Weber Deluxe PT is part of the main HV secondary. It can supply a few mA without drooping much. I remember -V tap of the PT in the Fender Bassman 100 drooped a lot even if I draw 2mA. It must be a separate winding from the HV secondary. I use the -45V tap to power the -V of the HV opamp. If this one use the HV secondary winding for the -45V tap, then I can do the same thing.