So I still want to replace the 6BQ5/EL84 since they are not even the same
brands but I looked at some web pages and tried to identify the 12AX7's I
have. On one tube I can make out a bit of the writing. What I can make out
seems to say in white paint
ECC83/12AX7
Made In
Holland
915
and in gold paint really faint
mCo
49B
that's all I can see.
I looked on the web for 12AX7 made in Holland and about all I come up with
is Amperex. I found this page with pictures
http://www.raretubes.com/XEECC83.htm
if you go there scroll down to the first three entries for Amperex they say
sq. getter, the insides of mine look like those with the very top piece
being a D shape with the little flat plate as shown. I am guessing that is
the square getter, I am not up on all the tube terms. So going by the
insides I would say that is what I have but what's left of the paint doesn't
look like it could have ever been that logo. Did any other tubes use guts
that looked like that? This guys got them listed at $150 - $175 a pair so I
guess I'll keep those. Someone mentioned that they last almost indefinitely?
Having fun,
Bryan
Durham, Oregon.
"Bryan McGivney" wrote in message
...
As for the tubes in it now, they sound pretty good but are mismatched, two
different brands or 6BQ5. The 12AX7's have all the writing rubbed off so I
figured I might as well replace them while I was at it since they don't
cost
all that much. Sort of a continuity of brands sort of thing more than
anything else.
Another question though, the phono input worked but it was very quiet and
sort of thin sounding. I don't have a schematic for the amp. I am guessing
that one 12AX7 is the phono stage and the other is the preamp stage. What
parts should I check first to get the phono stage working?
Do the caps I replaced need to run in for a bit before the sound will be
optimal?
TIA,
Bryan
"Fred Nachbaur" wrote in message
news:jI6_a.22$zE1.13@edtnps84...
Bryan McGivney wrote:
I got a Hoffman Stereo Hi-Fi console at the Goodwill because it had a
tube
amp in it and I wanted to pirate the amp for a fun project. Well I
pulled it
out of the console and fired it up and it hummed badly. It has two
multi
part can style caps on the chassis. I found caps at the local supply
house
and wired them in below the chassis to the terminals on the original
caps.
The amp sounds fine now but I figured I'd ask if there are any issues
with
not having removed the original caps from the circuit?
There might be down the road, if the old cap decides to short. That
being said, this used to be a pretty common service practise, and I've
never heard of a problem because of it. In my old age I'm getting
marginally more careful about stuff like this, so I think I'd physically
disconnect the old caps and put in a couple small terminal strips to
which to wire the new ones.
I hooked the caps up
with what I think is about 18ga speaker wire, with the copper
conductor
on
one side and silver conductor on the other. This shouldn't cause any
issues
should it?
Not other than being kind of ugly. ;-)
How hot might one expect the power transformer to get? I can touch it
but
it's hot enough you don't want to hold you finger on it long. My guess
is
around 110 - 120 degrees.
That sounds about right.
I have seen reference to adding a modern power socket like a computer
would
use and using the 3 prong grounded cord, grounding the chassis to help
reduce hum or noise. Is this usually OK or might I somehow get myself
into
trouble doing this?
You'll only get yourself in trouble if you wire it improperly. ;-)
I want to make a wooden enclosure for this with a metal screen top or
something like that. It seems that 17" is about the width of most
components?
Yes.
Reading the comments along with new tubes it looks like JJ/tesla might
be
the winner of not being the cheapest or the most expensive, just
inexpensive
yet good sound. I would need 2 x 12AX7 and 2 x 6BQ5. Should these work
well
or might I consider others?
What's wrong with the ones that are in there?
The amp has a switch for off, stereo 1, stereo 2, mono 1, and mono 2.
There
are only one set of speaker outputs. Is this maybe a setting for 4 ohm
and 8
ohm? I think the volume goes up a bit in the 1 positions.
It's *probably* meant for 8-ohm speakers. You can measure the DC
resistance of the speakers that came in the console to get a pretty good
idea. 8-ohm speakers will usually measure around 6 ohms DC resistance or
thereabouts.
Are there voltages I should be checking or stuff like that?
Wouldn't be a bad idea (and would be educational also) if you have the
schematic showing the typical voltages at various points.
There is a little pot on the back marked HUM what should I do with
this
adjustment?
Adjust for minimum hum.
Well it's late and I am sure there may be more questions but that's
all
I
can think of for now. More than enough for one post anyways.
Have fun. Be careful. Enjoy the music!
Cheers,
Fred
--
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