Rock-ola 1448 sound problem fixed....but HOW!!??
 

Hi group,
I've written before....I am not electromnically educated (this is why I
write the group for help/expertise). My Rock-ola 1448 has been
experiencing some "muddied" sounding sound recently. I had recently
switched volume controls, to "make-up" a new one with a new pot from
Vern Tisdale".
When I substituted the original pot/volume control, the sound became
"muddy" sounding.
I tried to fix it today, armed with everything EXCEPT a new nolume
control pot/wired harness.
I tried a new needle (with no success). I then checked tubes with my
reliable tube checker. One 6L6 (out of two) showed BAD (not weak;
bad!). Also one 6SN7 tube likewise showed BAD (not weak; but BAD
again!).
As I did not have additional tubes with me, all I could think to do was
switch each bad tube with the corresponding good tube's socket (as
there were two of each tube in question).
Lo and behold....the sound was no longer "muddy". It actually sounded
GOOD! Not understanding electronics (like a LOT of you do!), I wondered
how this could happen!?
If a tube is bad (and two WERE!), then how can switching the tube
sockets of each tube suddenly make a the sound come out GOOD! I really
don't understand how (maybe I don't WANT to understand how....but
REALLY I do/even if it is "above my head" electronically speaking). I
really don't want to get "yelled at" by Bill, Paul, or even Robin, by
asking them.
If my tube checker is accurate, and showed that each of the two tubes
(6L6 and 6SN7) were BAD, then how can simply switching the tubes in the
tube sockets make it sound great! I did re-build/re-cap the amplifier
several years ago. Please, since I am electronically "illiterate", shed
some light on this for me! I don't feel I'm asking for too much; just
an unknowing one's undersytanding of (simple?!) electronics. Trust me;
I can't find this out by reading a book (or a schematic/manual; even if
you can). Thanks, Rob

Rock-ola 1448 sound problem fixed....but HOW!!??
 

I don'tr put much trust in tube checkers. The real way to check is
substitude a known good tube. Many tube testers, especially drug store
types read the tubes as bad or weak to sell tubes. I think you had a
dirty tube socket and moving the tubes around scrapped some of the
corrosion off.
Charlie

Rock-ola 1448 sound problem fixed....but HOW!!??
 

I have Heathkit, B & K, and Eico tube testers. Generally if a tube
tests bad or weak on all 3 testers I consider it bad tube.

You certainly could have had tarnished pins in the tube sockets since
that's an old amplifier.

Rock-ola 1448 sound problem fixed....but HOW!!??
 

Thanks Ken......and you too, Charlie. It sounds like each of your
answers make a lot of sense.
The tube checker I have is a small compact model that does a large
variety of tube sizes....a Mercury, model 1101. I used to use a Hickock
(model 600?), but it quit working a number of years ago. I don't know
what went wrong with it, but it quit giving ANY reading for certain #s
of tubes, and I finally got frustrated enough to give up on it. I sure
wish I could find someone to troubleshoot it for me. The idea of trying
one tube in 2 or 3 different tube testers does sound like a great way
to go!
I guess the interesting thing to find out with the 1448 is what will
happen if I switch the two tubes around back the way they were (both
the 6L6 and the 6SN7) and see if the sound continues to be great, or if
it reverts back to the "muddy" sound. I may try that tomorrow night
when I go back for a Sunday visit. Thanks again you guys....you're the
best! Rob




I have Heathkit, B & K, and Eico tube testers. Generally if a tube
tests bad or weak on all 3 testers I consider it bad tube.

You certainly could have had tarnished pins in the tube sockets since
that's an old amplifier.

Rock-ola 1448 sound problem fixed....but HOW!!??
 

wrote:

Thanks Ken......and you too, Charlie. It sounds like each of your
answers make a lot of sense.
The tube checker I have is a small compact model that does a large
variety of tube sizes....a Mercury, model 1101. I used to use a Hickock
(model 600?), but it quit working a number of years ago. I don't know
what went wrong with it, but it quit giving ANY reading for certain #s
of tubes, and I finally got frustrated enough to give up on it. I sure
wish I could find someone to troubleshoot it for me. The idea of trying
one tube in 2 or 3 different tube testers does sound like a great way
to go!

First thing to suspect in a tube tester is the (surprise!) tube sockets.
If they have been used a lot (and frankly, in most cases, most of us
would never know, since most of us buy our testers second- or
third-hand), it would be the first thing to check. The 9-pin and
octal sockets are used most, naturally, and are often just plain worn
out. Try tilting the tube to the side a bit and see if you get any
jump in the needle reading.

--Bob

================================================== =====================
Bob Ellingson
Halted Specialties Co., Inc. http://www.halted.com
3500 Ryder St. (408) 732-1573
Santa Clara, Calif. 95051 USA (408) 732-6428 (FAX)