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 10th January 2014, 04:47 PM   #1
diyAudio Member
 
Join Date: Dec 2013
Default Lafayette LA-224a/b modernization?

Hello all,

New member here. Thanks to you guys I have a renewed interest in tube-type electronics, more specifically, audio amps. It's been many years (30+) since I've tinkered with such, but would like to one day (in the near future) build my own 25-30 WPC stereo amp. However, before diving in, I'd like to possibly "update" an old Lafayette LA-224A integrated amplifier that I've recently acquired. I've already brought it back from the dead by replacing all of the original, oil-filled caps with polyester/metal film caps from AES (Capacitor - Metal Film, Tubular, 400 V, .01F - 2.2F | Antique Electronic Supply). Most of the electrolytics have been replaced with modern electrolytic caps as well. The amp no longer red-plates and actually sounds quite nice, but part of me feels that I may have done more harm than good with my shotgun approach to the signal capacitors replacement.

I guess my question is a two-part one; 1.) Is it OK to replace all the original oil-filled caps with the metal film ones of proper size and voltage (albeit maybe not ideal)? and 2.) Can you guys recommend any "tweaks" to better this design? I've read elsewhere that the Lafayette iron is actually pretty decent.

Comments? Suggestions?

-Joe
Attached Images
File Type: jpg lafayettela224bsch.jpg (268.9 KB, 90 views)

Last edited by jbwebst; 10th January 2014 at 06:39 PM.
  Reply With Quote
Old 10th January 2014, 06:01 PM   #2
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Polyester caps are fine for everyday use. They can be very slightly non-linear so other dielectrics such as polypropylene or polycarbonate are used, but these can sometimes mean physically large caps which bring their own problems.
  Reply With Quote
Old 11th January 2014, 12:21 AM   #3
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
If you want to come close to the original voicing, use Soviet surplus K40 caps. in the coupling positions. K40s are hermetically sealed paper in oil (PIO) that don't spring leaks.

Converting the ceramic phono I/Ps to some sort of line level use seems indicated. My preference is to replace the source selector switch (about $5). You could convert the switch that controls the rumble filter to tape monitor loop duty.

The phono section heaters are AC heated. Unless you add a DC heater supply for the phono section, the ONLY tube to use in those positions is the Sovtek 12AX7LPS. The 'LPS is a genuine 7025 equivalent that contains a hum bucking, spiral wound, heater.
__________________
Eli D.
  Reply With Quote
Old 11th January 2014, 02:00 AM   #4
diyAudio Member
 
Join Date: Dec 2013
Whew... thanks guys, it's good to know that there's no harm done really. I've seen that the PIO caps are the way to go for the coupling positions, but of course it was after I rushed in and swapped the old ones out with the lesser caps! Any good online vendors for the K40s?

I was surprised that this thing is as quiet as it is - with no input and the volume maxed out, you really have to get up on the speakers to hear any kind of hum or buzz. The phono section however is a bit noisier so I'm anxious to try the 12AX7LPS in that position.

Here are a couple of pictures, the underside before I removed the death-caps & swapped out the others, and the top side during post-recapping testing - I guess this would have been a good time to re-purpose the ceramic input and swap out the source-selector switch, huh?
Attached Images
File Type: jpg DSCN2783 (Large).JPG (270.4 KB, 66 views)
File Type: jpg DSCN2855 (Large).JPG (303.5 KB, 61 views)
  Reply With Quote
Old 11th January 2014, 02:29 AM   #5
diyAudio Member
 
HollowState's Avatar
 
Join Date: Aug 2006
Location: Taxland, New Jersey
Quote:
Originally Posted by jbwebst View Post
... but of course it was after I rushed in and swapped the old ones out with the lesser caps!
They aren't "lesser", just different. PIO capacitors are slower. Paper is a poor dielectric and has a high dielectric absorption factor. This means they discharge slower which is heard as subdued high frequencies. A more mellow sound as the original had. Some folks like that, and some don't.
__________________
"It is hard to imagine a more stupid or more dangerous way of making decisions than by putting those decisions in the hands of people who pay no price for being wrong." ~Thomas Sowell
  Reply With Quote
Old 11th January 2014, 03:15 AM   #6
diyAudio Member
 
Junk Audio's Avatar
 
Join Date: Apr 2013
Location: Jersey
Listen to the amp for awhile, Don't get crazy on it. Change the caps, keep her running well. you will be moving on anyway. There's all kinds of stuff you will find as you continue with this hobby. Choose your battles wisely.

Take that from someone who hasn't always
  Reply With Quote
Old 11th January 2014, 12:18 PM   #7
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
I hope ALL OEM electrolytic caps. were replaced.

"Flea Pay" is where you look to find K40 PIO capacitors.

If the ceramic I/Ps are to be repurposed for additional line level duty, the source selector must be replaced. Mouser stock # 105-14572 is suitable and inexpensive. OTOH, if a tape monitor loop is desired, the existing source selector can be retained.

BTW, the recording O/Ps could be repurposed as I/Ps too.
__________________
Eli D.
  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
Lafayette KT600 lpd Swap Meet 0 4th June 2013 07:35 PM
Lafayette LA-234 Amplifier wrenchone Tubes / Valves 30 11th August 2009 06:33 PM
Powered up my Lafayette 224A for the first time! SigloOne Tubes / Valves 3 26th June 2008 02:18 AM
Lafayette LA-224 mavz Tubes / Valves 3 16th November 2005 10:32 AM
A Half ABC Lost In GC La La Land S.C Introductions 3 6th March 2004 03:06 PM


New To Site? Need Help?

All times are GMT. The time now is 04:31 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