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I repaired a vintage stereo for a guy and he picked it up and dropped off his vintage fender amp....it is all original....he wants it checked over to see if it needs any work and has stated that it is in good working condition.....it is all original......it has Mallory cathode bypass caps...the white ones with blue lettering....same for the bias cap..original diode there as well....all transformers are original....this thing has never been worked on.....should be nice to actually work on this.....it also has the original can filter cap as well.....even the pins on the tubes look in good condition....it also has the original blue caps on the tag board as well......the tag board is not warped like in other fender amps.....it has been well looked after......
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Take a look at the CapCan.....what's the date code on the can? 4-digit code....1st two numbers is the year of mfgr, last two numbers is the week of that year...such as 7734 = 1977, 34th week. As I recall, the Plastic encased electrolytic caps Mallory has there also have date codes on them. You're probably looking at 40 yr old caps thruout in the amp. I'd give a good long listen to this....powered up and let sit and idle for a good while. I'd hate to just suggest full re-capping the amp, though that could breathe new live into it. But.....if it sounds and remains stable, maybe just cleaning the pots and contacts.Logic is an organized way of going wrong with confidence -
Even if it "needs" fresh caps, be aware it WILL change the sound of the amp if you change them.Education is what you're left with after you have forgotten what you have learned.Comment
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I'd suggest - find out what your crustomer's intention is for this amp. Play it - or sell it? No surprise that deep pocketed amp collectors pay premium prices for collectible amps that are offered "as the factory made them" iow no mods, no "improvements", heck no repairs at all beyond maybe a change of tubes. If fetching a huge price for his prize is what he's looking for, just a quick checkup, maybe clean the pots and that's all. Let it run for an hour, see if the main filter cap heats up - if not, it's good enough. Last week I had a '69 Marshall 50W head come through here, same questions, same untouched condition. Turns out it's working wonderfully well after a bias adjust and a tiny dot of D-5 applied to the controls. It's for sale and the owner's gonna make bank on it I'm sure.Originally posted by bsco View Post
This isn't the future I signed up for.Comment
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he wants to keep it....he is concerned about failing caps after all these years...I will check it out and see what it sounds like....I plan on testing all the caps for correct value and esr.... maybe replace the two coupling caps to the output stages.........and that bias cap and diode as well...if the rest of the caps test good then I might leave it as is.....I will definately have a chat with him first before I do anything.....thanks for the advice..Originally posted by Leo_Gnardo View Post
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date code on the can cap is 7432......removed all the tubes and did a quick esr test on the caps...main filter cap.....esr approx 1.7 on all three sections..........all 25v/25uf caps between 1.5 and 1.7...with the exception of the bypass cap at pin 3 of V3....esr of 47.....bias filter cap 1.7 esr.....judging from that the only cap that shows a high esr is the one connected to V3/pin3.....however I will replace the bias filter cap along with the associated diode....and that one bypass cap....I also think I should replace the coupling caps from the inverter to the output tubes as well....no corrosion anywhere in the chassis....jacks are clean....pots feel nice and smooth.....should be a very quick repair....by the way...all the tubes also look original....Comment
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Checking caps for value? The caps they used back then had a tolerance of -20/+80%. Seriously. A cap that is 17uf instead of 20 is just not an issue. It could have been farther off when new.Education is what you're left with after you have forgotten what you have learned.Comment
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I would ESR test all of the 'lytics also. That will tell you if they are starting to dry out."I took a photo of my ohm meter... It didn't help." Enzo 8/20/22Comment
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they were the ones that I did an esr test on...I was going to do a capacitance test as well but according to Enzo it would be a waste of time....never the less I am still going to do that test as well as I am curious....thanks for the reply.....Originally posted by The Dude View PostComment
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Some very basic cap meters (like cap function on DMM) will report a high value for leaky caps. If you are aware of it, it can provide a useful function.
Most cap meters that measure ESR are not that type though.Originally posted by Enzo
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I have a separate cap meter...and a separate esr meter as well....and a couple of dmms.....I'llcheck it out tomorrow ...as I have aches and pains in both my arms...I guess due to the damp weather and has been like it now for awhile.....I use a heating pad to help with the issue and just waiting on the xray results to see what is the next step is going to be....thanks for the reply...Originally posted by g1 View Post
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I'm told alcohol works good for aches and pains, Bernie.
"I took a photo of my ohm meter... It didn't help." Enzo 8/20/22Comment
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And edibles, which are perfectly legal here now.
Originally posted by Enzo
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And gentle exercise. The 12 to 16 ounce lift, couple dozen reps each side, good as new in no time.Originally posted by The Dude View PostI'm told alcohol works good for aches and pains, Bernie.
This isn't the future I signed up for.Comment
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