Health Checkup: 1970 Marshall JMP!
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- Опубліковано 1 жов 2024
- In this video, Steve puts a super clean 1970 Marshall JMP through a health check while also running a fun experiment to test the original filter cap's performance specs vs their modern equivalents.
#marshall #vintageamps #amprepair #fryette #guitargear
The filter caps are not F&T they are to tall to be F&T . Tube amp DR buys them from China
Somehow just recently found the channel even though I’ve known about Fryette for a while. Loved every minute of this amp nerdage. What an amazing specimen that JMP is.
There's something about that red tolex 😍 and who needs a master volume when you have my PS-100!
In 1974 i was 14 and bought a new Marshall Super Lead 100 in red,i played it with two Ampeg V4 cabinets. Oh ive had so much great gear over the decades
Thats one sweet sounding Marshall
That's not hard to do.
Check out my latest video on the 1959RR amplifier
Sometimes I think, "I want to learn how to mod my own amps", THEN I hear Steve Fryette say a lot of big words and numbers, and then I think, "Uhhhhhh duhhhhhhhhh what!?!" 🤯
I know. im just adding a bright cap on to my Plexi clone….now I am like, “uhh what?”
Happy New Year fellas!
Great info on reforming filter caps.mits a shame that a lot of techs just replace the caps without a reason in these old amps. I have a 1980 JMP 2204 which still is stock . Filter caps and original Mullards are in great shape and the amp sounds great. I bought the amp new when I was 16
Wow, I rediscovered this video again, Nice work, amp sounds amazing. Most be the movement of the PT.
Cool stuff! Thanks for posting.
Suckers clean....I have a 71 needs a tune up
There's always a guy in every shop like him. Low blood pressure. articulate polite kinda boring goes home at night. lol
DUDES! What's the opening tune for this vid? Killer tones!
Hey buddy, it's from an album I did a long time ago that's up on Spotify. I keep trying to post the link but YT keeps deleting it. Anyway, the track is called "Snow White". Talk/hang soon!
It's an amazing track. The drums on that whole album are amazing as well. So tight and in your face. Good stuff Joe!
Hi Steve, beautiful job on this. Any idea where the client got the replacement head cabinet?
Really great episode! Definitely a nice opportunity to go deeper on the capacitor discussion. I love these videos!!
Really interesting episode! Thank you and Happy New Year to you guys!
Returned to stock nice.
The amp could have been dropped on the side in shipment that’s why the transformer might have shifted on impact. I have a combo that’s been dropped by airline luggage handlers - the transformers were almost torn off the chassis- the lugs bent, the chassis buckled and the 3/4” speaker baffle cracked. It is about 45lbs heavy and they probably decided to just throw the box it was in out of the plane right on tarmac instead of carrying it down.
Man would I love Steve to go through my Marshalls.......... Never seen caps reformed with that type of monitoring and diligence-- I hate to admit I work on my own amps when there's Steve out there......
Steve, you cracked me up. Thanks for the video! I always like to say "if you can hear it, you can measure it!" Thanks for the demonstration!
Sounds so good at the end, what speakers are in that cab?
Fryette/Fane F70G
I have found the exact same value issue lately on caps over 22uf, even Rubycon and Nichicon's. I purchased some from a "large" well known supplier, to replace components in some substitution devices, and found that the larger ones were mostly about 10% on the low side for 450V rated caps. They may get closer to value if formed to rated voltages, one device I just paralleled smaller values to get to the marked device values, the other one I think I ordered slightly larger values to get to the devices marked value.
These demonstrations are interesting but won't the amp present audible evidence that is symptomatic of bad filter capacitance that would lead to changing the capacitors rather than just replacing them due to their age?
Cool
You get some of the coolest amps on the bench... t-shirts ain't too shabby either 🍣
We get the coolest Ts!
Can you diagnose a bad filter capacitor from just looking at the ripple on the peaks of the output waveform - or is that just irrelevant? I have taken 2200 uF filter capacitors out of my Vox Pathfinder 15R and tested them on my little transistor all in one mk-172 tester and all the parameters tested great, capacitance, ESR, and a somewhat unknown quantity they label leakage? When I put it on a scope I get that same ripple that happens at the end of the clean headroom, and really bad deep into distortion. I am wondering if I should put higher quality and or higher rated capacitance capacitors? Or are the capacitors just bad and equivalent replacements are all that’s needed? Or do nothing at all -because it’s normal?
Leakage current is probably the most import of all the tests, so if that checks good, it's good, and your amp is running normally. Once you exceed the capacitors ability to smooth ripple, you have two choices: Accept that that's the way it's designed, or try to mitigate it with larger cap values. The second option will stiffen the amp and possibly kill the feel altogether.
@@FryetteAmps I worry about stiffening an amplifier. I heard that the first or in my case first pair of electrolytics that just go to the power amp section, they can be over spec without too much worry. It’s the following filtering caps for the preamp section where you want to be careful to not overfilter. Whether this true or not - I don’t have enough amplifiers under my belt to really know.?
My second thought was to overfilter to remove all ripples- then wire in two wire wound resistors just before the diode rectification bridge on both legs of the secondary side of the power transformer to mimic sag and to loosen the amp back up but without the ripple. Maybe this is just over working for little to no benefit? It just annoys me the ripple comes just at the on point of clipping at the power section with a max 11 watts of clean output in a 15 watts advertised amplifier. Thanks for the previous advice and anymore advice.
@@voxpathfinder15r The first two do all the work and have everything to do with ripple behavior. Not the downstream ones. Don't overthink it.
@@FryetteAmps I posted a video on my channel, perhaps first time in history someone put a Vox Pathfinder 15 on an oscilloscope and looking for totally clean headroom. Just curious what you think about the ripple the few times I show it distorting. Spoil alert, it maxed out at 11 watts before any harmonics set in. Not 15 watts like the adcopy stated. Thanks again Steve for your insight! Now I have to fiddle with the two pcb trimpots for the tremolo circuit since I just replaced the optocoupler. Then it goes back to my nephew as a gift for becoming a father any hour now! ua-cam.com/video/vJxVudGrqEs/v-deo.html
Sounds like Rock N Roll to me…
Quite a large bright cap in there! I put mine on the normal channel smaller is better none on bright channel then jump and use favorite pedal!
It’s the stock value.
@@FryetteAmps ok, just trying to see if you would connect your favorite boost pedal to the lead channel the way it is with that bright cap, then please get the smallest bright cap that works the best and take that large one off so there's no bright cap in the lead channel and the smallest one that works in the normal channel, add your favorite boost pedal and jump the channels and tell me if this sounds better than your favorite boost pedal in the lead channel with the factory bright cap
Thanks Steve I would be interested in your opinion
Does this turn dried up electrolytic paste back to a liquid state?
If the seal is good, the electrolyte is not drying out. As stated in the video, capacitor failure modes can be measured. A capacitor with dried electrolyte will read a significantly lower capacitance value and a higher ESR and leakage current.
@@FryetteAmps awesome! Thanks for the reply!
Steve what are your thoughts on substituting a 5751 tube for a 12ax7 tube? I have some old RCA 5751s in v1 of both of my amps; a 63 Fender Deluxe and a 71 Marshall. Am I doing something to hinder their performance or stressing them out in any negative way?
For what it's worth, Dave Friedman recommends a 5751 in V1 of some of his amps if you want a little more clean headroom. I have a 5751 in V1 of my Dirty Shirley Mini and can confirm it does indeed add a bit of extra clean headroom.
Transconductance on a 5751 is 1200umohs. That’s 20% lower than a 12AX7 at 1600. Many 12AX7s underperform, putting them in a similar category as 5751. Also, some tubes labeled 12AX7 are really 5751, such as Sovtek 12AX7WB. Meaning, you’re splitting hairs based on labeling. A 20% reduction in gain is not much different than turning the gain knob down a notch or so. Similar to the discussion about AX/AU/AT in this video, you may like a 5751 because the particular brand you chose has a tonal character you like unrelated to its gain. Moral: Use the specified tube or pick a suitable sub and set your amp accordingly. 😊
@@FryetteAmps thanks for the through reply. Truly appreciate you taking the time to explain things to a noob. I’m a software engineer have been for 15+ years but I’ve always liked hardware more. Doubled in CE in college. Sadly never got to use it nor apply it though. One of these days I hoping to revisit/relearn circuits and dive back into it so I can experiment and build some more clone pedals and maybe an amp one day.🤞 PS I also own a 71 dr103. Really appreciated and loved your guys’ episodes on the 50 and 100 watt Hiwatt and Sound City amps. Keep up the great work. 👍 👍
@@FryetteAmps Thanks for the pro info! VERY helpful. I suppose the 5751 in my DSM is a placebo effect of a sort? Really interesting stuff, I wonder what Dave Friedman would say about it, in this context?
@@dannbrauckmann1545 Ask him and let us know :)