Donor stereo 845 amp- now what!? - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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
Reply
 
Thread Tools Search this Thread
Old 19th October 2009, 06:02 PM   #1
diyAudio Member
 
Join Date: Feb 2006
Location: In the basement.
Default Donor stereo 845 amp- now what!?

Long story made short- I got this amp for about the price of shipping (essentially free). It did not include 845 tubes, but I had a pair of ShooGoo 845M's (metal plates) laying around. These tubes were a freebie too- jacked up by the previous owner; no doubt they were cooked on too high a voltage, but nothing that would indicate they would not perform. I plugged them in and fired up the amp. It played beautifully for approximately 5 minutes, and then a small bit of smoke was visible near the 845's. They didn't glow red, or seem unusually hot (no more than a standard 845 scenario). I cracked open the bottom cover and can find nothing burnt, or bad smelling. I haven't prodded around to check anything, but no obvious signs of BBQ could be found.

The amp is a "SOUNDTRACK ST-845" as sold on eBay out of Hong Kong. I had a pair of MingDa 845's that, while much better built, had a course grainy treble that would not go away. This soundtrack amp showed a lot of promise in its 5 minutes of glory. Barring the obvious need for a new pair of carbon plate 845 tubes. How do I fix it? What do I do? How could I improve it? I have no schematic for it, so if anyone has one- it would be a great help.
  Reply With Quote
Old 19th October 2009, 10:04 PM   #2
diyAudio Member
 
Richard Ellis's Avatar
 
Join Date: Sep 2006
Location: Mar del Plata, a BIG seasonal getaway city, can see the Ocean from our residence.
Default Soundtrack..

I looked in Ebay but nothing as you described. Do you have a schematic for this??? Some of the Chinese stuff comes & goes very quickly.leaving customers without recourse if they have problems. Someone here quite probably has one or has heard of your amp.....just a matter of time really, hang on.
Chinese gear is a good jumping off point to rebuild/modify/improve.
__________________________________________________ _________Rick...
  Reply With Quote
Old 19th October 2009, 10:21 PM   #3
diyAudio Member
 
Join Date: Apr 2003
Location: Portland,Oregon
Blog Entries: 4
Send a message via AIM to DigitalJunkie
Quote:
Originally Posted by blackeye*_0 View Post
I have no schematic for it, so if anyone has one- it would be a great help.

Grab your DMM,and start going over the resistors to make sure they match the value marked on them within a fair degree(10-20%),check any diodes,and perhaps give the caps a resistance check to make sure none are shorted/leaky -you'll likely have to lift one leg of each cap to effectively remove it from the circuit,otherwise you're just reading the circuit resistances,etc. The caps should read open-circuit,or at least several Megohms,very high resistance.
If all of that checks out,pop in some new tubes,and keep an eye on things for a while,just to make sure nothing funny happens.

I've had lots of funny smells and stuff come off of old tubes before,as they heat up the oil from your fingers,dirt,dust,etc. tends to burn off. I'm not sure I've ever seen any actually smoke,but I've never worked with 845's before,I assume these run pretty hot.
  Reply With Quote
Old 19th October 2009, 10:36 PM   #4
diyAudio Member
 
Join Date: Feb 2006
Location: In the basement.
Quote:
Originally Posted by Richard Ellis View Post
I looked in Ebay but nothing as you described. Do you have a schematic for this??? Some of the Chinese stuff comes & goes very quickly.leaving customers without recourse if they have problems. Someone here quite probably has one or has heard of your amp.....just a matter of time really, hang on.
Chinese gear is a good jumping off point to rebuild/modify/improve.
__________________________________________________ _________Rick...
Hi! It's like this one.
  Reply With Quote
Old 19th October 2009, 10:39 PM   #5
diyAudio Member
 
Join Date: Feb 2006
Location: In the basement.
Quote:
Originally Posted by DigitalJunkie View Post
Grab your DMM,and start going over the resistors to make sure they match the value marked on them within a fair degree(10-20%),check any diodes,and perhaps give the caps a resistance check to make sure none are shorted/leaky -you'll likely have to lift one leg of each cap to effectively remove it from the circuit,otherwise you're just reading the circuit resistances,etc. The caps should read open-circuit,or at least several Megohms,very high resistance.
If all of that checks out,pop in some new tubes,and keep an eye on things for a while,just to make sure nothing funny happens.

I've had lots of funny smells and stuff come off of old tubes before,as they heat up the oil from your fingers,dirt,dust,etc. tends to burn off. I'm not sure I've ever seen any actually smoke,but I've never worked with 845's before,I assume these run pretty hot.
OK, will do. I'll report back when finished...might take a while.

Yes, 845's are like the light bulbs on airfield landing strips; they can really light up a dark room and have the potential to get blazing hot. I was actually quite scared of my first one!
  Reply With Quote
Old 19th October 2009, 10:44 PM   #6
diyAudio Member
 
picowallspeaker's Avatar
 
Join Date: Apr 2007
Hello
A bad Output Trasformer ? So both , badly constructed ?
Did you get the demo CD
  Reply With Quote
Old 19th October 2009, 10:53 PM   #7
diyAudio Member
 
Richard Ellis's Avatar
 
Join Date: Sep 2006
Location: Mar del Plata, a BIG seasonal getaway city, can see the Ocean from our residence.
Default 845

Sorry didn't notice you didn't have a schematic. Things I did notice however.......perhaps the Chinese are stingy in the chassis department, but that chassis is WAY tight! The TXs' are potted of course so close proximity is sorta OK in that regard but the clearances of the 845s to that central TX is way too close....could the smoke you saw have originated by the paint burning off of that TX??? The corner??
Morgan Jones says, one and a half envelope widths is a good spacing, tube to tube.
This chassis throws out this spacing suggestion.

Just an idea...
__________________________________________________ ________Rick.....
  Reply With Quote
Old 20th October 2009, 12:29 AM   #8
diyAudio Member
 
Join Date: Feb 2006
Location: In the basement.
Quote:
Originally Posted by Richard Ellis View Post
Sorry didn't notice you didn't have a schematic. Things I did notice however.......perhaps the Chinese are stingy in the chassis department, but that chassis is WAY tight!
You should see under the hood! It's a layered bird's nest of corrective leads running back and forth because the layout is so lame.

Quote:
The TXs' are potted of course so close proximity is sorta OK in that regard but the clearances of the 845s to that central TX is way too close....
weird thing is the "central TX" is actually one of the output TX's. The power TX is one of the rear ones. Think I should switch it so both output TX's are on the back?

Quote:
could the smoke you saw have originated by the paint burning off of that TX??? The corner??
Just an idea...
__________________________________________________ ________Rick.....
Maybe- never thought about that....
  Reply With Quote
Old 20th October 2009, 08:02 PM   #9
diyAudio Member
 
Join Date: Feb 2006
Location: In the basement.
Ok, finished checking everything I could. My eyes are ready to pop out- very tedious. Everything seems fine. I wished I would have had some better caps for the power supply while I was at it...

I have a new set of 845's (carbon plates) on the way....
  Reply With Quote
Old 20th October 2009, 09:56 PM   #10
diyAudio Member
 
Join Date: Apr 2003
Location: Portland,Oregon
Blog Entries: 4
Send a message via AIM to DigitalJunkie
Cool. I know it's a bit of a pain,but sometimes components go poof,or other odd things happen that aren't readily visible..(FE,I've had resistors go open that looked fine,not charred or anything) So at least we're sure that's all OK.

Maybe just dirt/dust,or like Richard said,paint,burning off.
  Reply With Quote

Reply


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
Donor DVD player for DIY project smallangryboy Digital Source 3 29th December 2009 11:08 PM
Reprocessed for stereo, Rechanneled for stereo and Duophonic oldheathkitphil Analog Line Level 3 29th February 2008 01:20 PM
Donor H/K A224 Amp VeeDub Tubes / Valves 3 1st May 2007 08:47 AM
Which TT do I use as a donor for DIY TT? G Analogue Source 1 13th September 2004 04:43 AM


New To Site? Need Help?

All times are GMT. The time now is 06:31 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2