'69 SLP board to '68

Jack Hammer · Post by **Jack Hammer** » Sun Jul 06, 2008 9:26 am

Hi everyone!
recently I've bought a '69 PTP metroamp board used for my 1959SLP, I'd like to move to a '68 spec, what differences in tone?
thanks!

Flames1950 · Post by **Flames1950** » Sun Jul 06, 2008 9:30 am

A mid-to-late '68 spec preamp is the same as the '69.........although the preamp power filtering may be lower in some '68's.

Jack Hammer · Post by **Jack Hammer** » Sun Jul 06, 2008 12:25 pm

thanks!

although the preamp power filtering may be lower in some '68's.

what does this mean in terms of tone?

neikeel · Post by **neikeel** » Fri Aug 01, 2008 1:46 pm

Tone is quite similar.

The amp will feel less stiff and more fluid when you play it. It can also ghost if you go too low with filtering

68 filtering is 32/32 preamp, 48 PI (16+32 can in parallel) 16 screens(x2 32 in series) 50 mains (100 x2 in series)

The late 69s have x6 50uF cans

beaulieu · Post by **beaulieu** » Tue Aug 05, 2008 10:29 am

my 69 Marshall has 32preamp the 4 center caps are 200 uf @350 volts. and I think the PI is also the 200uf@350 volts. Does this sound correct for the PI (the cap in the corner by the P.T.) I changed the 4 center caps to 50x50. If I go back to the 200uf will I hear much of a difference using the 200's instead of the 50x50?? Opinions

neikeel · Post by **neikeel** » Tue Aug 05, 2008 2:24 pm

beaulieu wrote:my 69 Marshall has 32preamp the 4 center caps are 200 uf @350 volts. and I think the PI is also the 200uf@350 volts. Does this sound correct for the PI (the cap in the corner by the P.T.) I changed the 4 center caps to 50x50. If I go back to the 200uf will I hear much of a difference using the 200's instead of the 50x50?? Opinions

I would imagine your 200uF (350v) caps were wired in series to give 100uF of filtering at each point as 350v caps are far too low a rating for a PT that should be making around 480-490volts!

http://www.drtube.com/schematics/marshall/1959mk2u.gif

I presume your four 50uF cans in the middle were jumpered to make 100uF each and then hooked up in series with centre point tied as per this schematic. On this schematic the PI is also 100uF with the two +ves tied as well.

The 200uFs would feel stiffer and more immediate in their response not at all 'plexi-like' (assuming they were in good condition) I seem to remember their installation when you got it was pretty shocking!