Wiring Dagnall JTM45 / 50 (PT and OT) - Picture

jimapr · Post by **jimapr** » Wed Aug 08, 2007 12:33 pm

Hi,

I have a PT and OT from Dagnall to build my JTM45 Clone.
But I can

6string · Post by **6string** » Wed Aug 08, 2007 1:04 pm

I have an Offset reissue that has Dagnalls in it. I believe you are correct on the OT. I would add that white goes to V4 and red goes to V5.

I'm not sure about your PT though. Here's a couple of pics of whats in the OSRI.

MacGaden · Post by **MacGaden** » Wed Aug 08, 2007 1:35 pm

6string wrote:I have an Offset reissue that has Dagnalls in it.

Could you post some more pics of the board ? I

toner · Post by **toner** » Wed Aug 08, 2007 1:42 pm

[quote="MacGaden"]Could you post some more pics of the board ? I

jimapr · Post by **jimapr** » Wed Aug 08, 2007 2:22 pm

I cant say that my wiring of the PT is 100% identical with your wiring in your amp. I must see some other pictures... I cant track each cable.
But, thank you for that nice picture!

@Macgaden: I think this Board is a diy-board. Because somethimes you can see eyletts and sometimes turrets...

6string · Post by **6string** » Wed Aug 08, 2007 3:15 pm

Here's a pic of the board. Also of interest is the cap pic.

This amp belongs to a friend of mine. He has a couple of them, and he gave me this one to try out and possibly buy. It is the reason I decided to build a 45 myself. Figured I could build one at least as good if not better for less than half the price. It's a great sounding amp... has all NOS tubes in it. Not sure, but I think that flying resistor is a mod done by a tech here in Nashville who also put the NOS tubes in.

toner · Post by **toner** » Wed Aug 08, 2007 3:37 pm

Thanks for sharing 6string. It looks like that "flying resistor" got a little too close to the sun!

MacGaden · Post by **MacGaden** » Wed Aug 08, 2007 3:58 pm

Thanks for sharing, 6string.

That does

6string · Post by **6string** » Wed Aug 08, 2007 4:59 pm

It's a limited edition handwired Marshall. Only 300 were made. 250 came to the USA and 50 went to Japan.
http://namm.harmony-central.com/SNAMM00 ... M450S.html
http://www.marshallamps.com/downloads/f ... %20hbk.pdf

Not sure about the cap on V2. I believe Marshall puts the 1K resistors across the speaker jacks for OT protection. I went ahead and put one on my build.

novosibir · Post by **novosibir** » Wed Aug 08, 2007 5:33 pm

The 1K on the speaker jacks was stock in some JTM45's from the mid 60' - although it doesn't protect the OT against anything - way too big!

The 'flying' 1K has to be rated for 5W, but this one is a 1W or 2W only!

The cap on V2 is something like a 'sweet' or 'fizzy' cap.

Larry

6string · Post by **6string** » Thu Aug 09, 2007 9:33 am

Any idea as to why they put the 1K resistors there?

neikeel · Post by **neikeel** » Thu Aug 30, 2007 6:28 am

My JTM45RI from 1989 also had one of those resistors, I thought that it was a mod until I saw some mid 60s schems.

The one on mine was an old fashioned 5watt matt light green wire wound job (not a Welwyn tho').

I remember some discussion between Flames and George about with and with out it. Concensus was the amp sounded more open without.

Not sure of real (electronic reality) as opposed to desired (not thought out bassman derivatives!) function of these resisitors but these amps do have 470ohm grid resistors too on the schematics so they may be part of OT protection if a valve goes pop. Isn't the resistor on the jacks to try to present some load to the OT in case of the speaker lead comong adrift? It looks pretty puny too so I do not imagine it would last long!

Help Larry