Health Checkup: 1979 Marshall JMP 50w
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- Опубліковано 20 січ 2023
- Joey Brasler brings his 1979 Marshall JMP by the shop for Steve to give some TLC. There's discussion about the mod Steve installed in the amp 35 years ago, the general maintenance Alexander Dumble performed on the amp as well as the usual bench nerdery and bad jokes that happen during these episodes. Enjoy!
#joeybrasler #dumble #fryette #marshalljmp #amprepair #vintageamps - Розваги
this is great stuff! As a '78 JMP owner, super interesting.
I said it before and i will say it again Steve Fryette is like a extremely talented Brain surgeon but with amps!
I can even envision him with the surgeon scrubs on while he works in amps! 😁
Love it, fellas. My 78 2203 is my all time fav amp, nice to see this 2204 still making people smile.
Now that's how you set up your controls on a 1979 JMP 50!
I miss u guys so much. I love your senses of humor
Very nice video. Talking about preamp tubes, in 2021 I purchased a bunch of Shuguang 12AX7B and JJ ECC83S and ECC803S tubes. ( Unfortunately no date codes to tell when those tubes were in fact manufactured) I have heard many stories that Shuguangs sound brighter than JJ tubes and I have noticed that I can hear that difference by my ears as well. I tested those tubes in a test circuit and standard Deluxe preamp circuit feeding them from signal generator and observed output signal using a good oscilloscope and I can confirm that the HF bandwith of Shuguangs of those measured individual tubes is clearly wider than the BW of JJ ECC803S and ECC83S tubes in same test circuit. It practically means that the input capacitance of Shuguangs is smaller than that of JJ ECC8O3S tubes. However, the (middle and upper middle range 400-4000Hz, I did not measure low frequencies) gain (Vout/Vin) of those especially ECC803S tubes was noticably bigger as well than the voltage gain of Shuguangs in same circuit and because of that the bigger gain increases the total input (Miller) capacitance as well. The results were very clear and repeatable. In that test circuit the 3dB BW of Shuguangs went to around 67 kHz when JJ ECC803S tubes went to just only around 45 kHz. (Grid stopper value of test circuit input was around 45kohm.)
I was very surprised because I did not expect that those differences could make such a clear audible difference but because you can compensate the volume by volume or gain pots but you usually cannot change the circuit component (plate resistor, cathode resistor) values without physically changing them, the tubes with different gain or/and input capacitance sound different in the SAME circuit. If for example plate or cathode resistor values could be adjusted to give the same Vout/Vin ratio, the differences of individual tube properties would probably not make such a noticable difference. But if you put a different tube individual with different gain and/or input Miller capacitance into the same circuit, it really can make a difference.
Damn i would kill to have Steve Fryette's amp knowledge!
Always good info and fun.
Joe! Don't go! What a cool video! Old-school, LA amp tweakery at it's finest. More, more!
Bob! Come over & jam again!
Amp sounded AMAZING! So, if I'm understanding this correctly, the 10K cathode on V1A was changed to a 2.2K with a 1uF bypass cap and also the 100K plate resistor feeding V1A was bypassed by a disc cap (value wasn't mentioned)? Such simple mods made that amp sound MEAN. Thanks for the video fellas!
You deduce correctly. V1A bypass cap is .001/1KV. Gain pot bypass cap is also .001/1KV. We got it twisted in the vid. The original pot bypass cap was .0047 - more upper mid forward, which Steve's Esquire didn't need, and which turned out to be perfect for Joey.
Sounds awesome… But… Bypassing the plate resistors can couple mains hum through into the signal unless the b+ there is perfectly filtered (which it definitely isn’t on a 50w).
It’s slightly quieter to go to v1a’s cathode ground point, or even just the between the plate and cathode pins on the tube socket itself. It’s all the same result frequency wise any which way you go about the snubbing anyways.
This was super fun to watch and interesting! I just started getting into amp modding about 5 years ago so stuff like this is better than gold! What I would give to work in a shop like that with someone that’s as knowledgeable as Steve. Glad I found the channel! 🤘
Great Episode !! I miss hearing this amp down at the local spot.
That’s the sound of rock right there.
Just subscribed, learning a lot from you Steve. Really good stuff.
Very excited for this video. I have that year make and model Marshall and after not knowing for years it was rewired to plexi specs it was rewired to its stock specs with what my amp tech called a Van Halen mod or something. I can’t believe how long I wasn’t experiencing the true identity of that amp. Frankly, my PS-100 has really been the key to unlocking its tones for me. Oh I almost forgot to mention that it had an fx loop in a prior life but had been reversed before I bought it used so it bears the scars.
...Off on both of those. Now I got it. Cool tweak Steve. Thanks for sharing.
That sounded amazing! Now I need a JMP with this mod.
These videos are awesome !!!! Keep them coming.
I have old Pittbull CL-50
I think it needs a health checkup !!!
I’d love to send him my Montgomery Ward head to check.
cool to see a sound city in the workshop
SSS (Still Stevie Spec) Nice job, sounded great! My tinnitus is jealous…..
That amp sounds damn good.
joey is a 👑 among men.
Early JCM 800. Marshall still in contract with Distributor I think. The 2nd stage with 10k is a cold clipper it helps for even harmonics [asymmetrical] clips on the other side of waveform [cutoff]. That's why it took a while for commercially produced cascaded preamps. If I'm right these were special orders to somebody. Still under the JMP [4 Holer]. Remember around 80-81 It went JCM 800 he had to let his contract expire. Then be free to make model changes. Or get sued. That was always a problem being in England. It's an example of Business man vs. Artist. That's why he allowed certain players with a proto type. But not to the masses.
Wow. Now I want to mod my 2104. This sounds amazing. Very Van Halen (in the right hands).
I use to go to 9:30 club all the time.
That CV4004 tube in v3 is actually a Mullard!
Wow i thinking about the 6550 tubes! Back in the day i got a new Marshall JCM 800 50watt that had 6550 power tubes in it and i hated that amp it just didn't sound good! So i had a tech go back with EL34's in it after that the amp sounded okay i still was not happy with it. I later sold it. them years sown the road i did get a new marshall jcm 800 50 watt that came stock with El34's in that sounded good! I kick myself later telling it go too! that was back in the 80
s and 90's them so back 5 years ago everybody was talking about blackstar how good there are so i got one HT stage 100 mk2 that amp is the bigest peace a shit i ever played threw! this year i'm getting a better amp!
Try a set of 6CA7 tubes you will be amazed I run them in my 1978 100 watt JMP
I've been wondering a few things about the Powerstation. How do the depth and presence knobs change the tone? Secondly, where should they be set for a flat response?
Is the 8ohm load you reference purely resistive or a reactive load? IE do you use a power station as the speaker load or one of the resistors mounted on the bench. Thank.
V3 is a Mullard box plate. Not made in Blackburn but still a legendary 12ax7.
What a cool story. Sure wouldnt mind trying out the "Dickies Mod." Hey Steve. Is it just setting up the first stage cathode with 2.2k/1uf and changing the bright cap from 1nf to 470pf? I think thats what I heard.
I had one of those Marshall’s. Never got along with the power transformer putting out only 390v on the plates.
Too mushy for me.
I like more around 460v for some good headroom and punch.
I have a 75 1987 unmodded running into a 74 1960ax with original creambacks
Whoah watching it again I was way off. Is it 820/1uf on the cathode, 4700 bright cap and a plate snubber (470-1000pf ish)
I had a marshall once that came with a marshall gold letter 12ax7 in V3, I was never able to get as good of a sound without that gold letter in there !!! I think it was a balanced tube (??!!??!!??)
Ok, I looked up from soldering my parts board when I heard, “through atmosphere NFB network”.
🤘🤘🤘🤘
What is the music for the first 10 seconds?
Joe composes all the music for our videos.
@@FryetteAmps Thank you, found Joe's channel and the actual tune, really sounds great!
I have a 1979 JMP50w too. Should sell it being I don't use it.
Get a Power Station and enjoy playing the amp!
@@FryetteAmps
First I gotta do a cap and tube service on the old girl.
Marsh ll
I think it sounded best the initial time the guitar was plugged in. I didn’t care for it much through the Power Station. too much gain too much tone change
but thats just me😊
he is touching all over the amp, isn't he afraid he will get electrocuted?
Does he look like he's afraid of getting electrocuted?
@@FryetteAmps everybody else is saying be careful touching inside the amp, because there is still charge, but this guy is maybe immune?
Why be a tone snob ?
Some of us need a loop.
You can still be a tone snob and have a loop. That's what Power Stations are for. I have six heads all running through a KHE switcher. Some with FX loops and some without. I don't use the loops in any of them though. I use the loop in the PS as a global FX loop so no matter which head I select via the KHE switcher, I get the same FX loop via the PS. Works perfectly for me.
I'm superstitious about adding circuitry to my favorite amps, especially since I almost never need a loop. As @bradleywood1499 says, if I needed effects with this amp - and I have on a couple of occasions - I would take a speaker out to a Power Station and use a 2nd cab - which is a glorious sound!
I learned that Marshall amps are friggin' great sounding AS-IS. Stop f--ling modding when you do not need to do so!
(adjust your eq, your guitar volume, and use the right pickups! dammit!)