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Old 10th January 2014, 04:47 PM   #1
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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?

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Last edited by jbwebst; 10th January 2014 at 06:39 PM.
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Old 10th January 2014, 06:01 PM   #2
DF96 is offline DF96  England
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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.
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Old 11th January 2014, 12:21 AM   #3
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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.
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Old 11th January 2014, 02:00 AM   #4
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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?
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File Type: jpg DSCN2855 (Large).JPG (303.5 KB, 61 views)
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Old 11th January 2014, 02:29 AM   #5
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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
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Old 11th January 2014, 03:15 AM   #6
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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
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Old 11th January 2014, 12:18 PM   #7
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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.
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