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

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

Postby Roe » Mon Jan 26, 2009 7:26 am

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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.

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.

The voltages are higher than expected. with 230+ v wall power into the 240v primary and the 490v secondary, the heater voltage is 6.6v and the b+ about 488v biased at 60%. I wonder if heyboer have mixed up the colour codes on the 220, 230 or 240v primaries?

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.
Roe
 
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Re: early 67 45/100 w/el34s, 119 OT, 43PT, aluminuim chassis

Postby Roe » Mon Feb 02, 2009 4:09 pm

this amp is breaking in now. hardly any ghosting at all. filtering is:

16x16 pre
30 pi
23 screens
47 mains

I will change the two latter when sozo releases his 32uf caps
Roe
 
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Re: early 67 45/100 w/el34s, 119 OT, 43PT, aluminuim chassis

Postby Roe » Tue Mar 03, 2009 5:15 pm

more pics:
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Roe
 
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Re: early 67 45/100 w/el34s, 119 OT, 43PT, aluminuim chassis

Postby David B » Mon Mar 09, 2009 10:45 pm

Nice pair of amps, what speakers ya using?
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Re: early 67 45/100 w/el34s, 119 OT, 43PT, aluminuim chassis

Postby Roe » Tue Mar 10, 2009 9:56 am

Hi, mostly scumback H75s - sometimes a H55 or a M75 or even some alnico speaker
Roe
 
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