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 Post subject: Old amp has grainy sound, Need to fix, Help, Pics posted,
PostPosted: Feb Wed 22, 2012 4:11 am 
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Joined: Jan Sun 24, 2010 10:52 pm
Posts: 4280
Location: Phila Pa
I don't have a wiring diagram or much equipment since I am moving across the state and stuff is at both houses now,
I tested all the tubes on my TV-3 tester and they all tested good with no shorts,
The Amp has been recapped by another and since I have no diagram I am a bit losses, I was hoping that someone could suggest somewhere to look.
The Amp has good tone and volume, But it's grainy sounding, I have tested it with other speakers and same result.
The tube line up is,
6SJ7
6C5
6SN7
6N6
6N6
5V4
The Amp is a Hollywood Electronics studio serial #22
Thats all the info I have on it.
Any suggestions would be helpful.
Thanks
I would love this amp to sound right!
Peter


Last edited by pred on Feb Wed 22, 2012 10:14 pm, edited 1 time in total.

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 Post subject: Re: Old amp has grainy sound, Need to fix, Help
PostPosted: Feb Wed 22, 2012 5:53 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3051
Location: Boston, MA USA
There are several things it could be. I would start by taking some voltage measurements. We can just about guess at the circuit by the types of tubes used, but to have a schematic with the proper voltages would be helpful.

When you get set up, maybe you could post some under-chassis photos to provide some basic information, like what kind of bias, tranformer or RC coupling, etc.

-David


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 Post subject: Re: Old amp has grainy sound, Need to fix, Help
PostPosted: Feb Wed 22, 2012 6:43 am 
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Location: near ST Louis Mo
My first thought is that there should be 6L6's in the amp instead of 6N6's.

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 Post subject: Re: Old amp has grainy sound, Need to fix, Help
PostPosted: Feb Wed 22, 2012 7:00 am 
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Joined: May Sat 14, 2011 5:42 am
Posts: 3002
Location: Ft Worth TX
As above, confirm tube complement. Confirm cathode resistor values.


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 Post subject: Re: Old amp has grainy sound, Need to fix, Help
PostPosted: Feb Wed 22, 2012 12:26 pm 
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Joined: Jan Sun 24, 2010 10:52 pm
Posts: 4280
Location: Phila Pa
I will get some voltages after work today,
I was thinking that the 6N6s were only 1 year but there is no tube sub in the tube sub book I own, I was thinking I could toss some 6L6s in there and see what happens :mrgreen: But that may not be my best idea of the day,
I will also get some pics this afternoon, Please check back.
Peter


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 Post subject: Re: Old amp has grainy sound, Need to fix, Help
PostPosted: Feb Wed 22, 2012 2:22 pm 
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Location: Hawthorne, Ca
I don't know if 6L6's could be used for a replacement for 6N6's as they are completely different tubes. I have a Silvertone 4588A that uses 6N6's for the out put and it sounds great, the problem is they are expensive. I've also heard that the 6N6 has an internal resistor that can go bad which causes problems, but I can't say for sure that's correct. I'm sure there is a way to convert the amp to 6L6's with some work. I'm thinking there may be something miswired or incorrect parts used as replacements causing the grainy sound. Harry


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 Post subject: Re: Old amp has grainy sound, Need to fix, Help
PostPosted: Feb Wed 22, 2012 2:51 pm 
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Location: Utica, NY 13502 (USA)
Wondering how long ago the amp was recapped and what type of caps were used. If paper caps were used, they could very well be leaky.

Dave


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 Post subject: Re: Old amp has grainy sound, Need to fix, Help
PostPosted: Feb Wed 22, 2012 4:45 pm 
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Joined: Jan Sun 24, 2010 10:52 pm
Posts: 4280
Location: Phila Pa
Dave Doughty wrote:
Wondering how long ago the amp was recapped and what type of caps were used. If paper caps were used, they could very well be leaky.

Dave

I would guess it was recapped pretty reciently, Maybe a few months to a couple years.
Anyone have a diagram for a Hollywood #22 Amp?
I cant seem to find any info on them.
Will get some pics up in a few hours,
Please stay tuned.
Peter


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 Post subject: Re: Old amp has grainy sound, Need to fix, Help
PostPosted: Feb Wed 22, 2012 7:04 pm 
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Joined: Sep Thu 23, 2010 6:37 am
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Location: Powell River BC Canada
If the amp has ample loudness yet sounds distorted, try reducing the signal
level you are feeding it with. You might be overloading the first ( 6SJ7 ? ) stage.
The volume control may be after the first stage.

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 Post subject: Re: Old amp has grainy sound, Need to fix, Help
PostPosted: Feb Wed 22, 2012 8:05 pm 
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Location: Detroit, MI USA
I have had several radios with push-pull 6N6's in the output stage, and none sounded as good as a conventional design using 6V6's. They seem to distort very easily and never sound "clean".

It's possible after ruling out everything else to rewire for 6V6, 6F6, or 6L6 types you just have to add a cathode resistor and make certain the bias is correct for the new tubes.

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Experience is what you gain when the results aren't what you were expecting.


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 Post subject: Re: Old amp has grainy sound, Need to fix, Help
PostPosted: Feb Wed 22, 2012 8:19 pm 
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Location: Warner Robins, GA
Could be a resistor.


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 Post subject: Re: Old amp has grainy sound, Need to fix, Help
PostPosted: Feb Wed 22, 2012 8:39 pm 
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Joined: Nov Sat 27, 2010 6:15 pm
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Wow, never heard of 6N6, although I hae a quad of 6M6 somewhere, supposed to be like 6L6. Anyone have more info?


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 Post subject: Re: Old amp has grainy sound, Need to fix, Help
PostPosted: Feb Wed 22, 2012 8:54 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Boston, MA USA
I had never heard of it either, but I did find a data sheet:

http://frank.pocnet.net/sheets/084/6/6N6G.pdf

It's a very weird tube, in fact two triodes in an envelope with coupling built in. Claims to not require external biasing. I don't think it would be easy to substitute any other tube.

-David


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 Post subject: Re: Old amp has grainy sound, Need to fix, Help
PostPosted: Feb Wed 22, 2012 9:16 pm 
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Location: Warner Robins, GA
Maybe a dual triode TV sweep tube would work?


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 Post subject: Re: Old amp has grainy sound, Need to fix, Help
PostPosted: Feb Wed 22, 2012 9:36 pm 
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Joined: Nov Sat 27, 2010 6:15 pm
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Gotta be another version of 6B5, should have known, another Dog!


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 Post subject: Re: Old amp has grainy sound, Need to fix, Help
PostPosted: Feb Wed 22, 2012 10:13 pm 
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Joined: Jan Sun 24, 2010 10:52 pm
Posts: 4280
Location: Phila Pa
Here are some pics.
What can I do and look for,
I checked resistors and they all look good to me,
I could change the caps that look real nice.
Any suggestions?
Peter


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 Post subject: Re: Old amp has grainy sound, Need to fix, Help, Pics posted
PostPosted: Feb Thu 23, 2012 4:50 am 
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Joined: Feb Thu 24, 2011 1:29 am
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Location: Dallas, TX - in the city but with bobcats and coyotes
Two notes from here:
White wire back to interstage xfmr must be to a feedback winding, yes?
Also, what is the number on the beautiful output xfmr and what impedance speaker are you playing it into?

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 Post subject: Re: Old amp has grainy sound, Need to fix, Help, Pics posted
PostPosted: Feb Thu 23, 2012 6:03 am 
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Posts: 21103
Location: Detroit, MI USA
Start diagnosis by feeding a clean signal from an audio generator into the input, and follow it through the unit with a scope to determine where it is first distorted. That will give you a clue where to look for a fix.

Also, the rectangular Micamold wirewound resistor with a blue dot seen at lower center of under chassis view, next to one of the 6N6 sockets, how is it connected?

You may need to sit down and draw the schematic by hand so we can see if it is reasonable.

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Experience is what you gain when the results aren't what you were expecting.


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 Post subject: Re: Old amp has grainy sound, Need to fix, Help, Pics posted
PostPosted: Feb Thu 23, 2012 2:58 pm 
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Joined: Feb Thu 24, 2011 1:29 am
Posts: 3021
Location: Dallas, TX - in the city but with bobcats and coyotes
With feedback as such it is possibly less of a problem, but, I would look up transformer (or take measurements to calculate turns ratio) and determine proper load impedance before doing too much else. You could chase your tail all day if the root cause was "vastly" improper loading. Just my thoughts, others will disagree. Then, I'd listen to it. If it still sounds poorly, I'd break out the dummy load and scope.
Just another thought - does the speaker that you are using sound good to begin with?
Good learnin' on finals biasing is available here: http://tone-lizard.com/Oscilloscopes.htm#Bassman
Go to almost the bottom of the page and look at the three links under the heading "The Amplifiers".

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 Post subject: Re: Old amp has grainy sound, Need to fix, Help, Pics posted
PostPosted: Feb Fri 24, 2012 1:59 am 
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Joined: Jan Sun 24, 2010 10:52 pm
Posts: 4280
Location: Phila Pa
More pics to look at.
Something I noticed is that on one tube the small 250K resistor goes from pin 1 + 2 to pin 5 and the other tube goes from 1 to 6 with a 20K and pin 5 with a 250K,,, seems like they are a tad different,
Also, I am now wondering,,,, I bought the AMP as you see it, I wonder if the right tubes are in the right spots, Tough for me to tell without a schematic.
I am sorry I haven't had time to get in there, Work is getting in the way of life,
Peter


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Last edited by pred on Feb Fri 24, 2012 3:06 am, edited 2 times in total.
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