Vintage Asylum

Classic gear from yesteryear; vintage audio standing the test of time.

Return to Vintage Asylum

Message Sort: Post Order or Asylum Reverse Threaded

Heathkit AA-121 underside pics & PS question

71.209.22.2
Posted on December 13, 2014 at 14:47:03
lektrik
Audiophile

Posts: 447
Joined: May 31, 2002
 Anyone with a Heathkit AA-121 have some underside pics of the area under the can capacitors? I have picked up a partially worked on AA-121 that had some missing parts, clipped wires, and questionable replacements of parts.

I've followed the schematic and I think I have things hooked up correctly, but I would like to have what you might call a 'second opinion', which some pictures would supply.

The two front 200uf cans have been replaced with bridged JJ 100/100uf 500V caps held in place with clamps. The two rear 150uf cans were re-stuffed with Nichicon 350V caps.

Question: Are the two 200uf caps 'hot' like the two 150uf ones. I don't think they are, but they are separated from the chassis like the 150ufs, so I'm not sure about them.

I'd like to get this one fixed, but since it was incomplete when I got it, it may take a while to get it right. Thanks for your help.

Larry D.

 

Hide full thread outline!
    ...
Hre's one from a long-ago auction, posted on December 14, 2014 at 10:06:51
ToddM
Audiophile

Posts: 1612
Location: Atlanta, USA
Joined: May 15, 2001
Contributor
  Since: June 13, 2005
 Mine is modded, but using the same values, and like yours, it was a bit hacky when I got it, so I used this sort of thing as a sanity check.




 

Nice!, posted on December 14, 2014 at 21:43:36
lektrik
Audiophile

Posts: 447
Joined: May 31, 2002
 Thanks for the picture! I'll bring the amp out to compare it to your pic to see what's wired right or wrong. That's what I needed.

I'm waiting for some 100K 2 watt resistors to come in before I go and bring it up on a variac. I'll let you know how it goes.

Larry D.

 

RE: Nice!, posted on December 14, 2014 at 23:30:49
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 Larry
That has a doubler just like the Macs,Citations,and some Eicos.One cap is insulated with cardboard but I would put in a pair of 820uf or at the very least 470uf nichicons.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Nice!, posted on December 15, 2014 at 20:59:16
lektrik
Audiophile

Posts: 447
Joined: May 31, 2002
 Right now I'm doing a minimal re-cap of the amp to see if it even works. I hate getting stuff that was hacked and left unfinished. I don't do enough work on these to get good at figuring problems out like this one.

This is supposed to be a very nice sounding amp. I've gotta borrow a quad of EL34s from a local buddy to check it out. If it works well and I like it, then I may go ahead and try upping the capacitance or changing over to poly caps.

Larry D.

 

It's alive!!!, posted on January 11, 2015 at 20:59:44
lektrik
Audiophile

Posts: 447
Joined: May 31, 2002
 I finally borrowed some EL34s from my fellow audio nut, er I mean enthusiast and plugged them and a pair of 6AN8s into the AA-121, brought it up slowly on a variac and eventually out came music when I got to around 60 volts. There is a little distortion in the left channel, but at least at this point I know the transformers are good and that everything is back to being hooked up properly.
I'll balance the voltages and the bias tomorrow, but what a relief to know its a good amp with no major problems. Yes!

Larry D.

 

RE: It's alive!!!, posted on January 11, 2015 at 21:23:46
mark.korda@myfairpoint.net
Audiophile

Posts: 1253
Location: Maine
Joined: August 16, 2011
 Todd, that was one of the nicest wiring and soldering jobs I've ever seen! Lektrik, that picture is better than the manual.Can I ask you guys how important is it to, in a rebuild,to replace resistors in vintage tube amps even though they test all right? Thanks...Mark Korda

 

RE: It's alive!!!, posted on January 12, 2015 at 16:24:42
lektrik
Audiophile

Posts: 447
Joined: May 31, 2002
 From the information I've gathered over the years it would not hurt to replace the carbon comp resistors with newer type carbon films or metal films (in the power supply) because the carbon comps tend to drift out of spec with heavy usage.

I don't remember the reason why, but some people don't like the rectangular 'casket' type resistors and would replace them with a Mills type wirewound resistor. I usually leave the casket type alone if they're in spec.

Larry D.

 

Wow! This is a great amp!, posted on February 27, 2015 at 22:15:52
lektrik
Audiophile

Posts: 447
Joined: May 31, 2002
 Here it is the end of February and I finally got to sit down and listen to this amplifier on a rebuilt set of Infinity RSMs and I am impressed! There is a lot of 'air' and dynamics with this amp. I started listening to one of my reference CDs and I just wanted to keep listening because it sounded so good.
I'll play it for a while and let the caps burn-in and keep an ear open for any changes. If I hear none then that will be fine since I already like it where it's at. I'm glad someone gave me this to fix up. I wasn't expecting much since it was free, but boy was I wrong (there's a first time for everything). AA-121 is highly recommended here!

Larry D.

 

Page processed in 0.021 seconds.

[ Top Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]