heathkit SA2 - 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 April 2013, 02:49 PM   #1
rock12 is offline rock12  United States
diyAudio Member
 
Join Date: Nov 2010
Location: midland mi
Default heathkit SA2

Recently rebuilt a heathkit SA2 using there detailed manual( they even tell you how long to cut and where to bend every wire). New caps and resitors were installed. I used the hum trim pots but there still remains some hum how do I trace this down? I own a digital meter and soldering iron
Attached Images
File Type: jpg IMG_0380.jpg (293.3 KB, 119 views)
  Reply With Quote
Old 19th April 2013, 03:07 PM   #2
rmyauck is offline rmyauck  Canada
diyAudio Member
 
Join Date: Apr 2009
Is that a before pic, as the round orange item looks like a original cap? What about the topside can caps(s)?
  Reply With Quote
Old 19th April 2013, 03:42 PM   #3
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Check the heater wiring for really tight twists and small loops, especially near the input stages. The part shown in the photo doesn't look brilliant.
  Reply With Quote
Old 19th April 2013, 03:53 PM   #4
diyAudio Member
 
trobbins's Avatar
 
Join Date: Feb 2009
Location: Melbourne, Oz
Localising the source/cause is important - as many red herrings can be suggested as a solution.

Try and check if it is just from the input stage (short the signal or turn down a pot after the input stage). Try and check if it isn't the input stage input wiring (short the input valve grid to 0V). Run the input stage heater from a battery (this will indicate if it is heater related).
  Reply With Quote
Old 20th April 2013, 01:33 AM   #5
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
ALL electrolytic caps. must replaced. The orange "thingy" a previous poster pointed at looks like a 'lytic to me. Jim McShane is a good source for tubes, parts, and advice. The can cap. previously mentioned is (IMO) best replaced by a clamp mounted part occupying that opening. Mr. McShane stocks that sort of stuff.

What, if any, source was used, when the hum was detected? You need shorting plugs in the I/P jacks to test, without a signal source being attached.

Take a close look at the schematic. Notice AC heating in the phono section. Only a 7025 equivalent, with its spiral wound, hum bucking, heater, has a ghost of a chance of being quiet enough. Buy a pair of phono grade, current production, Sovtek 12AX7LPS tubes from McShane. That Saratov, Russia, made variant IS a genuine 7025 equivalent, whose price is reasonable too.

Heath's gain structure is wretched! They attenuate line level signals and then amplify them with the 2nd gain block of the phono section. That wreaks havoc with the S/N ratio. That can be "cured" by replacing the source selector switch with an inexpensive Lorlin brand part from Mouser and a bit of rewiring.

The "laundry list" goes on. Install a proper, 3 wire, safety grounded, power cord. Get "120" VAC away from the front panel by disconnecting the on off switch on the treble control. Install either a slide or rocker switch in an opening currently occupied by a convenience outlet, to control the on/off function. Add the uploaded SS diode tweak to the 5AR4 socket, with UF4007s, not noisy 1N4007s. The tweak may allow you to squeeze some extra time out of the old stock tube and is essential to reliable operation of the current production Sovtek 5AR4, which is the best of the affordable stock. NOS 5AR4s are outrageously expensive.

BTW, if you plan on recording LPs to another medium, a much more capable phono section, whose O/P impedance is low, is needed. Yes, I have a candidate for that job, should it be needed.
Attached Images
File Type: jpg tuberectifier-diodemod.jpg (141.4 KB, 85 views)
__________________
Eli D.
  Reply With Quote
Old 20th April 2013, 11:43 AM   #6
rock12 is offline rock12  United States
diyAudio Member
 
Join Date: Nov 2010
Location: midland mi
Sorry should have labeled the picture as a before pic. Thanks for the advise it was a great project to learn from. I will try some changes and get back
  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
heathkit SA2 rock12 Tubes / Valves 4 6th June 2012 11:53 AM
Heathkit variac ixe13 Tubes / Valves 3 3rd April 2008 05:01 AM
heathkit sa2 - new question -=Zepplock=- Tubes / Valves 8 5th September 2006 05:29 PM
Perreaux sa2 laz Solid State 3 26th February 2004 11:12 AM


New To Site? Need Help?

All times are GMT. The time now is 01:54 PM.


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