JTM45 board differs from BB

[Mars Hall]

Up until now, I always thought the front end of the BB and JTM45's were the same. While populating my BBri board, I noticed a difference in the amount of .022 caps, on the front end, of both circuits. The JTM45 board layout shows 5 of the .022's on the front, (before the 3 larger .1) the BBri board layout has 6.

I bought premium Sozo's for this project. I only purchased five .022 caps. Of the six .022's on the front end of the BBri layout, which would be the one to substitute with a standard Sozo? Are all six caps tone shaping? If needed I'll order a sixth .022 from Sozo, but if one can be substituted that will move this project along a lot quicker.

My buddy Jim (jbzoso2002) noticed another difference. The 500pf bright cap is in a different place. On the JTM45 layout it shows on the right leg of the 270k resistor pyramid. The BBri layout shows it on the left. Is the BBri layout correct, or should that cap be moved?

[chubs]

The bluesbreaker has a tremolo circuit... Probably the extra cap there...

which layout are you using?

[Mars Hall]

I'm using the layout posted on wiki. If you look at both circuits the BBri has more .022's on the left of the .1's. If one of those six go to the tremolo circuit, I want to know which one, so I don't waste a premium sozo where it will not benefit the tone. I don't want to use premium sozo on the tremolo circuit.

[chubs]

can you post a link to the layout... wiki you mean wikipedia...? can't find it.

[VelvetGeorge]

http://metroamp.com/wiki/index.php/Blue ... ssue_board" onclick="window.open(this.href);return false;

[chubs]

Ya, you're correct... there is an extra 0.022uf in the there... regardless of the tremolo... Now you got me curisous...

[908ssp]

My amp and the pictures of originals I have on file don't have the third one from the left on the board. The rest looks close the trem section is different but you don't care about that.

[chubs]

Weird... bypass cap? error?

[Puerco]

I don't want to promote Ceriatone here on the Metro forum but their Bluesbreaker layout doesn't show that extra cap, the main board is just like a normal JTM45 (except for the bias pot that is placed between the power tubes on top of the chassis) http://www.ceriatone.com/images/layoutP ... iatone.jpg" onclick="window.open(this.href);return false;

What are those grey caps in that original bluesbreaker picture 908ssp posted? I've seen them in pictures of very early Offset's too while others had the mustard caps we all know and love.

[908ssp]

I was told they are RS oil/paper capacitors. I replaced the .018 Mustards with those .o22 Russian oil/paper caps in my Offset [which actually measure .019] and they do sound warmer smoother a bit less gain. I'll leave them in see if they hold up ok.

[Puerco]

RS PIO caps, they must be harder to find than mustards..
I'm still planning a Offset replica and am still thinking what components would be a)vintage correct, b)sound best c) are still available (or have good replacements).
Also I'm surprised to see those RS PIO caps in a bluesbreaker, thought they switched to mustards by then.

[Roe]

the extra cap can be found on several of the later bluesbreaker amps. see here:



http://amparchives.com/album/Marshall/B ... 5_B_L.html

http://amparchives.com/album/Marshall/B ... 1BB09.html

http://amparchives.com/album/Marshall/B ... 05534.html



also, the pics at amp archives shows several bluesbreakers running a 8 ohm load (two 15 ohm speakers in parallell). wonder if the RS OTs were wired for 16 ohms as usuall

[chubs]

Thing is... what does the cap do... is it a bypass cap? A tone stack cap... ??

[908ssp]

the extra cap can be found on several of the later bluesbreaker amps. see here:



http://amparchives.com/album/Marshall/B ... 5_B_L.html

http://amparchives.com/album/Marshall/B ... 1BB09.html

http://amparchives.com/album/Marshall/B ... 05534.html



also, the pics at amp archives shows several bluesbreakers running a 8 ohm load (two 15 ohm speakers in parallell). wonder if the RS OTs were wired for 16 ohms as usuall

Only the first link has the extra .022 the other two don't. At least I don't see them.

[Mars Hall]

From looking at pictures of other builds, I deduced the 3rd cap from the left is connected to the back of the intensity pot. I noticed the same gray wire on my amp, it's routed behind the pots to the other end of the amp.

http://forum.metroamp.com/viewtopic.php?f=15&t=21935" onclick="window.open(this.href);return false;