No doubt it is worth it to keep good things running. I agree. Especially cars! I cherish my 6 speed manual transmission as Corp America has all but eliminated it from every car to streamline production and ensure the highest profits. If my amp stopped working, I would pay up to get it repaired. But in my case, everything works and I enjoy what I hear. So paying $1200 (and probably more) to have it overhauled is not on my list of things to spend $$$$ on in this now very expensive world we now live in. I once almost bought an amp off Audiogon and when I asked the seller why he was selling, he told me he had taken his 25 year old amp to have it overhauled with all new caps and resistors and had all the contacts re-soldered. He said he didn't like the sound of the amp when he got it back. Many times I have had things repaired (not just audio gear) and didn't like how it performed when I got it back. So now that I am close to retirement age, I don't change anything in life that is working and I am happy with it. There is no "Spot on", everyone's situation is different. If you like what you have, leave it alone and enjoy the music.
Panel life?
- Thread starter zinda
- Start date
Help Support MartinLogan Audio Owners Forum:
All of this equipment we use is machinery and it wears out with use there is no disputing that fact no matter how you slice it and as it wears out the performance degrades that’s all I’m saying. Enjoy your equipment.
This thread has morphed from 'panel life' to 'equipment life' it seems, but it's all good stuff.
I too am a proponent of keeping old amps alive and well, even if they aren't the expensive 'high-end' models.
I'm sharing my recapping story below so that others will know that even someone with no electronics experience can recap an amp, if you're careful, without breaking the bank. Below is a link to my recapping thread, with photos, on the CarverSite:
https://thecarversite.com/topic/1116-recapping-a-tfm-25-for-dummies/#comment-7094
When building my system in 2008, I purchased three used Carver TFM-25's on Ebay for around $900 (total), and refurbished them. As I recall, I spent about $120 per amp on parts.
Even though I had no electronics experience and no clue how to refurbish an amp, I could solder pretty well, and I found service manuals and inspiration on the CarverSite Forum, and dived in. Fortunately all three amps were still in working order so all I needed to do was replace the components most prone to fail with age.
In each amp I replaced all 39 electrolytic caps, checked resistors, and replaced any that looked even a little toasty (even if they measured good).
A typical refurb would not involve raplacing any transitors, but in my case there was a TMF-25-2 Service Bulletin reliability upgrade, which I did concurrently, and it consisted of replacing (4) pre-driver transistors, replacing several resistors with 'flame proof' versions, and lofting all of the replaced components 3/8" above the board to prevent heat-damage to the board.
Before starting, I drained power from all the caps using a 100 watt light bulb. The big power caps lit the bulb brightly for a few seconds before dimming down as their charge drained.
Before removing any caps I marked the tops of every cap (with a Magic marker) so that I would not get confused about which caps I had already replaced and those I had not yet replaced.
Throughout the refurb I had the amp connected to speakers, and I would replace four or five components, and then do a sound check with music. That way; if something went wrong I wouldn't have far to backtrack to find the problem.
After each sound check, I drained power from all the caps again before continuing.
The last step was setting the idle currents to bias the transistors on each channel. There was an easy procedure for this in the Service Manual, which involved conncting DVM leads to check points on the board, turning the amp on and letting it warm up for five minutes, then using a tiny screw driver to adjust bias pots unitl the DVM reads 1.0 mOhms.
That's all there was to refurbishing a Carver TFM-25.
I found the experience really empowering. All three amps played wonderfully, and are still playing wonderfully to this day.
To my ears; the amps sounded OK before the recap but definitely more dynamic and alive after the recap.
Hey, go for it!
I too am a proponent of keeping old amps alive and well, even if they aren't the expensive 'high-end' models.
I'm sharing my recapping story below so that others will know that even someone with no electronics experience can recap an amp, if you're careful, without breaking the bank. Below is a link to my recapping thread, with photos, on the CarverSite:
https://thecarversite.com/topic/1116-recapping-a-tfm-25-for-dummies/#comment-7094
When building my system in 2008, I purchased three used Carver TFM-25's on Ebay for around $900 (total), and refurbished them. As I recall, I spent about $120 per amp on parts.
Even though I had no electronics experience and no clue how to refurbish an amp, I could solder pretty well, and I found service manuals and inspiration on the CarverSite Forum, and dived in. Fortunately all three amps were still in working order so all I needed to do was replace the components most prone to fail with age.
In each amp I replaced all 39 electrolytic caps, checked resistors, and replaced any that looked even a little toasty (even if they measured good).
A typical refurb would not involve raplacing any transitors, but in my case there was a TMF-25-2 Service Bulletin reliability upgrade, which I did concurrently, and it consisted of replacing (4) pre-driver transistors, replacing several resistors with 'flame proof' versions, and lofting all of the replaced components 3/8" above the board to prevent heat-damage to the board.
Before starting, I drained power from all the caps using a 100 watt light bulb. The big power caps lit the bulb brightly for a few seconds before dimming down as their charge drained.
Before removing any caps I marked the tops of every cap (with a Magic marker) so that I would not get confused about which caps I had already replaced and those I had not yet replaced.
Throughout the refurb I had the amp connected to speakers, and I would replace four or five components, and then do a sound check with music. That way; if something went wrong I wouldn't have far to backtrack to find the problem.
After each sound check, I drained power from all the caps again before continuing.
The last step was setting the idle currents to bias the transistors on each channel. There was an easy procedure for this in the Service Manual, which involved conncting DVM leads to check points on the board, turning the amp on and letting it warm up for five minutes, then using a tiny screw driver to adjust bias pots unitl the DVM reads 1.0 mOhms.
That's all there was to refurbishing a Carver TFM-25.
I found the experience really empowering. All three amps played wonderfully, and are still playing wonderfully to this day.
To my ears; the amps sounded OK before the recap but definitely more dynamic and alive after the recap.
Hey, go for it!
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Yeah, if you're happy with it and it's running fine I probably wouldn't do a thing.
BobLobLaw
Member
The main (but no only) factors responsible for panel degradation are moisture, UV exposure and environmental contamination (dust, smoke, etc).
Moisture is by far the biggest enemy and will degrade the panel faster than anything else. An air conditioned room is about all you need to prevent moisture degradation.
UV light degrades the vapor deposited coating but glass just so happens to filter out the UV responsible for the degradation. So in front of a window is fine as long as the sun filters through glass first. No direct sun contact.
When the panels are built, the film gets coated by hand with a sponge dipped in a mixture of graphite and alcohol that then gets spread onto the surface of the film. This helps prolong the life of the film by adding a 2nd coating to the already vapor deposited PET film (Polyethylene terephthalate)
The symptoms of environmental degradation, (usually dust) will be a crackling sound from the panel when powered on. Dust carries a static charge and is naturally attacted to the positively charged film when it's in use, eventually becoming a pathway to ground causing the crackling sound. This was minimized years ago when ML started using a sensing power supply that allows the panel to discharge and power down when not in use, therefore losing its static attraction to dust. Vacuum both the front and back of the panel with a strong vacuum to get rid of most crackling.
The symptoms of degradation due to moisture will simply be a loss of volume output.
Rarely do both panels degrade at exactly the same rate so one panel will usually start to sound quiter than the other when they need replaced.
Moisture is by far the biggest enemy and will degrade the panel faster than anything else. An air conditioned room is about all you need to prevent moisture degradation.
UV light degrades the vapor deposited coating but glass just so happens to filter out the UV responsible for the degradation. So in front of a window is fine as long as the sun filters through glass first. No direct sun contact.
When the panels are built, the film gets coated by hand with a sponge dipped in a mixture of graphite and alcohol that then gets spread onto the surface of the film. This helps prolong the life of the film by adding a 2nd coating to the already vapor deposited PET film (Polyethylene terephthalate)
The symptoms of environmental degradation, (usually dust) will be a crackling sound from the panel when powered on. Dust carries a static charge and is naturally attacted to the positively charged film when it's in use, eventually becoming a pathway to ground causing the crackling sound. This was minimized years ago when ML started using a sensing power supply that allows the panel to discharge and power down when not in use, therefore losing its static attraction to dust. Vacuum both the front and back of the panel with a strong vacuum to get rid of most crackling.
The symptoms of degradation due to moisture will simply be a loss of volume output.
Rarely do both panels degrade at exactly the same rate so one panel will usually start to sound quiter than the other when they need replaced.
I had heard that a secondary graphite slurry coating was applied and you just confirmed it.
Now I have a question:
My one and only experience with ML panels was replacing the diaphragm in an older ML Theater panel. The diaphragm in that panel had a lighter coloration tint in the areas over the spars and about 3/16" on either side. I concluded that those areas over the spars had been masked off before the slurry coating was applied.
I speculated that these areas were masked off either to facilitate better bonding to the mating spars (on the front stator), or as a barrier against charge migrating up the spar edges to the front stator, as might occur if dust builds up along the spar edges. Just a theory...
Do you happen to know if those areas were masked off, and if so, for what purpose?
BobLobLaw
Member
The film is masked around the edges and over every spar, prior to adding the graphite coating to keep the coating away from the edges and off the spars. When the masking is removed it also removes the vapor deposited coating effectively turning the panel from 1 large speaker into several small individual cells or windows.
The edge of the panel is where the powder coat is the thinnest so removing the vapor deposit from the edge of the film prevents the voltage from the film from ever arcing over to the edge of the panel should the powder coat ever be too thin and not caught during QC.
That makes sense then, as the diaphragm-to-stator spacing is closest over the spars, and charge tends to migrate to areas closest to a stator.
Thanks for the info!
Really fantastic info, new member from Lawrence, Kansas
Tosh
Well-known member
Here's a pic showing the graphite between the masked-off areas. I didn't realize the vapor coating is removed during the assembly...
