early 67 45/100 w/el34s, 119 OT, 43PT, aluminuim chassis

[Roe]

Hi, I've just built the very first el34 100w amp. these uses aluminium chassis, and drake 1202-119 OT and 1204-43PT. I don't know of anyone else that have done this but it I'll be pretty similair to my 66 jtm 45/100 with the exception of choke (20h 70mA RS v. 3h), OT (4k primary v. 1.75k), kt66s v. el34s, preamp filtering (16uf v. 32+32uf), indicator lamp (orange v. red), cab (vox vents v the later cab). mixer resistors are 270k rather than 470k I believe. Originals seems to have NFB (27k) connected to speaker out.

I choose this amp after talking to a local amp guru. he recommended aluminium chassis over steel. also, he didn't recommend the voltage doubler and the dual rectifier (saying that the dual rectifier will result in a slower attack).

nevertheless, I might end up trying a few things that are not historically correct. I tend to like 50uf on the mains rather than 32uf, and I like to reduce the .1uf pi coupling caps or the 220k bias splitter resistors. otherwise the bass knob is almost useless at high volumes.

I'm using marstran trannies, old mustards and old tubes. resistors will be CF expcept CC for NFB, slope resistor and possibly the 820ohm and 100k resistors with long legs (like old marshalls).

the amp sounds a little cleaner than expected. but she is biased cold now. she ghosts a little with el34 with the volume at 10, esp. with the normal channels. the ghosting is bearable. has a dirtyish sound that reminds me of doyle bramhall II and some of hendrix distorted sounds from 67 and early 68.

Right now I have the stock preamp filtering (32+32uf). PI filtering is a just below stock (30uf - originals were 32uf, not 16uf like the later amps). However, I've upped the screens filtering to 23uf and the mains to 47uf.

http://folk.ntnu.no/roef/67_009

she starts to sound real good. barely any ghosting with my gretsch but a little with a sg, esp. in the neck position.
I'm running shitty ecc83s and george's winged =C= el34s. I bias a 30ma at 488v, i.e. 60% diss. 60% sounded way better than 50%. my weber mass 150 gets hot. sustain is good even at home levels. I get some feedback in my kitchen.

[doctord02]

If it's anything like my '66 JTM 100 Super PA, you are pushing it with the 150 watt Mass... My tech measured the output on mine and it was apx 100+ watts at the onset of clipping and a whopping 218 watts when dimed...

Something to consider.

[Roe]

yes, I know
my 66 45/100 with kt66s isnt as powerful as this one - the main difference is the 66 has a 4k ot primary whereas the 67 has 1.7k primary.

[Roe]

as opposed to the later jtm100s with the voltage doubler, this amp hardly ghosts at all I guess that the 1204-43PT with center tap helps. any comments?

[David Root]

Roe, did your guru say why he thought dual rectifiers would reduce attack? I would have thought the opposite, if anything.

Or was it only with a voltage doubler AND the dual rectifier?

[Roe]

I guess he said it should have a slower attack if the rectifiers are in series

[Roe]

more pics:
http://folk.ntnu.no/roef/jtm100stop
http://folk.ntnu.no/roef/backjtm100s
http://folk.ntnu.no/roef/gutsboth
http://folk.ntnu.no/roef/sideboth
http://folk.ntnu.no/roef/frontboth