Music Man Sixty Five
Arfa Daily
surprised to see a plate voltage of 730 on the two 6CA7 / EL34 output
pentodes. That is some serious HT, and I'm sure rather higher than I
remember seeing typically on any similar amps. The problem was low distorted
audio, and was down to an O/C screen (G2) feed resistor. Full normal
operation was restored once this had been replaced. G2 volts were around 360
when it was running normally. The bias was about -36v. I actually looked
this configuration up, and it just falls within the maximum specs for those
tubes, which are quoted at 800v on-load plate voltage max. At this level of
plate, G2 and bias, the quoted max output is 100 watts. That's pretty good
going from a single pair. Most amps from that era used two pair to get that
sort of power.
I guess the name "Sixty Five" relates to this amp's claimed output power,
but even that is PDG from a single pair, given that most amps of a similar
configuration are typically only capable of 30 watts or so.
The output tubes that are in it look quite old, but they are delivering the
goods, and are pretty reasonably balanced, so I am reluctant to recommend
replacement as a standard 'service' option whilst it's in, given the dubious
quality and reliability of many tubes these days, even when running at
relatively low levels of plate voltage up to say 500v. Anybody know much
about these amps ? Not terribly common this side of the pond - or at least
I've not had the pleasure of seeing many from this manufacturer over the
years ...
Arfa
Meat Plow
> Just had one of these lovely old amps across the bench, and was
> extremely surprised to see a plate voltage of 730 on the two 6CA7 / EL34
> output pentodes.
That's what they run em at. What did you need to know about them, I used
to own a 112 combo 65/35 watter. Probably very similar.
--
Live Fast, Die Young and Leave a Pretty Corpse
Arfa Daily
"Meat Plow" <mhy...@yahoo.com> wrote in message
news:pan.2010.09...@hahahahahahahah.nutz.I.am...
> On Wed, 22 Sep 2010 18:13:49 +0100, Arfa Daily wrote:
>
>> Just had one of these lovely old amps across the bench, and was
>> extremely surprised to see a plate voltage of 730 on the two 6CA7 / EL34
>> output pentodes.
>
> That's what they run em at. What did you need to know about them, I used
> to own a 112 combo 65/35 watter. Probably very similar.
>
>
>
Nothing particularly. Their website has all the schematics for free
download, and I fixed all the problems on this one. I was just interested to
see if anyone had any stories about them - or the manufacturer in general -
as it's not a brand commonly seen here.
Arfa
Meat Plow
I didn't care for the sound of my 112 combo. It was tolerable with some
external FX. Played a sand colored 130 watt head didn't care for it.
Company was founded incognito by Leo Fender who at the time had a 10 year
non-compete clause with CBS. The early amps were better, newer being
hybrid with tube output. Pedal Steel guitar players did like them
however. And they made a decent keyboard amp.
Arfa Daily
Interesting. This one was a hybrid using some early can-type opamps in the
front end. The schematics showed three different output configurations, two
of which employed FETs in the driver/phase splitter. The version that I was
repairing had a conventional 12AX7 phase splitter. I don't play guitar
myself, but keep an instrument in the workshop for test purposes. I have to
say that the sound from this amp was 'harsh'. Not distorted or anything,
just not the 'smooth' sound that you normally associate with a tube output
stage. not 'melodic' sounding is about the best way I can put it. I guess
that's why they might be considered good keyboard amps. I've always thought
that the 'hard' sound of transistor power amps, suits keyboards well.
Arfa