Help Vintage Guitar Hummer - diyAudio
Go Back   Home > Forums > Live Sound > Instruments and Amps
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Instruments and Amps Everything that makes music, Especially including instrument amps.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Closed Thread
 
Thread Tools Search this Thread
Old 18th July 2005, 03:54 PM   #1
Trout is offline Trout  United States
diyAudio Member
 
Trout's Avatar
 
Join Date: Nov 2004
Location: Midwest Madman
Question Help Vintage Guitar Hummer

Hi Guys,

Im Stumped on trying to repair/restore a vintage {Guessing} 1960-1963 Kay Practice Amp Model #703.
I was at an auction this saturday on a 150 year old farm. Saw this little baby sitting there and just had to have it. Its exactly the same model I had as a kid when I got my first guitar.

Figureing the worst, I tested the tubes, All RCA originals and found them well within good usable condition. No shorts, about 85% out of 100 possible on my tester.

Everything inside looked to be clean, Nothing looked changed or burnt so I plugged her in. 10 or so seconds Its Humming very loud!! I quick shut her down figuring a cap job is in order. SO, I replace The paper caps with nice nos spragues orange drops of correct values. Then move on to the power supply muliticap.

40,40,30 - 150V
I just happen to have a brand new in box NOS sprague atoms in my vintage supply! SWEEET.

So, I proceed to swap out the old Ajax multicap with the NOS Sprague.
Plug her in, About 10 seconds HUMMMMMMMMMMMMMM again.
In Fact no change at all.

It is a VERY Loud hum, And Sounds like its at about Full volume when you touch the end of a open guitar cord !

I Have the schematic as it was pasted inside the unit, And Have also found it online.

(schematic removed by Moderators for safety reasons)

Heres A Review from Harmony central on this amp, I remember it as being exactly as this reviewer describes:


Sound Quality: 9
'93 American Std. Tele.
For clean to slightly dirty blues/jazz and rock this little gem shines.
It had a pretty loud buzz until I replaced a multi-stage electrolytic capacitor and put in a three prong power cord. Now, it's very quiet up till about 8 on the volume at which point a very quiet buzz manifests. Probably my unshielded guitar and not the amp.
I'm continually impressed with the gorgeous, snappy clean sounds I get out of this amp.
The distortion is mild, but I suppose it would respond well to a tube screamer. I don't own a distortion pedal so...
Still using the original speaker, but I might upgrade in the future.


Right Now Mines apart on the bench, So I will post more pictures later. Prime objective right now is to figure out what I must Be Missing.
Any Input would Be GREAT!!
Gene
 
Old 18th July 2005, 04:35 PM   #2
Trout is offline Trout  United States
diyAudio Member
 
Trout's Avatar
 
Join Date: Nov 2004
Location: Midwest Madman
Heres the parts list, I marked the replaced item.

Parts List
Gene
 
Old 18th July 2005, 05:08 PM   #3
diyAudio Member
 
Join Date: Apr 2003
Location: Portland,Oregon
Blog Entries: 4
Send a message via AIM to DigitalJunkie
Ahh,the old 60FX5 tube!
I once made a stereo SE headphone amp with a pair.(~1W per channel- dangerously loud on headphones!!)

Just a note,I dunno if I had bad luck or what,but every 60FX5 I laid my hands on was *really* microphonic!
 
Old 18th July 2005, 05:20 PM   #4
diyAudio Member
 
Frank Berry's Avatar
 
Join Date: Sep 2003
Location: Midland, Michigan
That is a dangerous amplifier. It has no isolation from the mains.

The very first thing that you should do is use an isolation transformer on the powerline.
__________________
Frank
 
Old 18th July 2005, 06:23 PM   #5
Trout is offline Trout  United States
diyAudio Member
 
Trout's Avatar
 
Join Date: Nov 2004
Location: Midwest Madman
Quote:
Originally posted by Frank Berry
That is a dangerous amplifier. It has no isolation from the mains.

The very first thing that you should do is use an isolation transformer on the powerline.
Yes, this is very True.

BUT, for the sake of originality I wish just to restore it to working condition. Seeing as its never going to be used for anything but occasionally rare Mic'd recording and conversation piece.

Right now, I have just completed testing the resistors only to find no issues. Yet I still only get a constant Hum.
This is not affected by volume or tone control. Nor Instrument plugged in or not plugged in. The only thing left would be the ceramic caps. Or Possibly a tube that even though its testing correctly, Has an issue. I am really stumped.
Gene
 
Old 18th July 2005, 06:42 PM   #6
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK


If this amplifier does not have an isolation transformer then it is extremely dangerous and you do not have the necessary knowledge to be fiddling with it. Cut the mains lead off and keep it as a conversation piece. It doesn't matter how rarely you propose to use it. Lethal only needs to happen once.

__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
 
Old 18th July 2005, 09:00 PM   #7
diyAudio Member
 
Miles Prower's Avatar
 
Join Date: May 2005
Location: USA
Blog Entries: 7
Here is what I would do with that. Rewire the power supply to include a 1:1 isolation xfmr, full wave SS bridge (you could use SiC Schotky's for an even quieter PS) and keep the 36AM3 as heater ballast, leaving the plate and cathode disconnected. That way, you preserve the aesthetics of the thing, remove the "suicide box" aspect of the original design, and have a much quieter PS, in that the filter capacitors will be twice as effective with double the ripple frequency.

That kind of xfmr-less PS is a disaster waiting to happen. If you connect the hot side of the main to the chassis ground, your guitar will also be at 120V(ac) to ground.

An utterly irresponsible, dumb-@553d design, if you ask me.
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com
 
Old 18th July 2005, 09:05 PM   #8
diyAudio Member
 
Miles Prower's Avatar
 
Join Date: May 2005
Location: USA
Blog Entries: 7
If this amplifier does not have an isolation transformer then it is extremely dangerous and you do not have the necessary knowledge to be fiddling with it.

No, EC8010, he said he was going to use it with a guitar, not a fiddle.
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com
 
Old 18th July 2005, 09:15 PM   #9
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
Quote:
Originally posted by Miles Prower
No, EC8010, he said he was going to use it with a guitar, not a fiddle.
If cracking gags like that isn't already a sinbinnable offence then it soon will be...
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
 
Old 18th July 2005, 09:28 PM   #10
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 2
I'm closing the thread and removing the stunningly dangerous linked schematic.
__________________
"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
 

Closed Thread


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
4x12 Guitar cab using guitar and bass speakers help andrewskaterrr Instruments and Amps 15 24th April 2009 12:43 AM
Hummer H3 enclosure Treiff74 Car Audio 4 21st March 2009 04:53 PM
vintage cd-80 honsten Digital Source 1 31st July 2004 07:29 PM
Vintage OPT stigla Tubes / Valves 2 10th June 2004 09:21 PM
12" Vintage Guitar Cabs rossco Everything Else 1 17th October 2003 09:23 AM


New To Site? Need Help?

All times are GMT. The time now is 10:57 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2016 DragonByte Technologies Ltd.
Copyright 1999-2016 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki