JCM800 2204 Cameron HG Jose build thread

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Congrats.. I just fore up the amp.. LOL
Some Zeners look like regular Diodes and the others have the redish orange color.. Do they all sound the same??
 
midnightlaundry said:
Congrats.. I just fore up the amp.. LOL
Some Zeners look like regular Diodes and the others have the redish orange color.. Do they all sound the same??
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It depends on what the clipping voltage threshold is on different zener diodes as to how the clip and sound. Technically the usable range for zener diodes on a Jose or even a JCM800 style master like Dave Friedman uses is 20volts down to 5volts. You basically have to try them to see what your ear likes

The 20V/20V clips the least with the least amount of gain/compression to the tone and as you go down in voltage the clipping,gain and compression increases.

I like 20V and 16V zeners and recently tried out the 2N5400 transistor wired to be used for diodes which supposedly clips at a bout a 8-11V threshold when compared to zeners and it does sound better than I remembered.

You can also get into infinite asymmetrical clipping like a 20V/16V zener setups it all depends on what you like from your experiments.
 
harddriver said:
Isn't the MPSA06 the one Friedman uses for the SAT switch in the BE100? I think I tried that one as well, I'll have to dig through my diode bins again and see if I have an MPSA06.....

Does the 2N5401 have some attributes the 2N5400 doesn't? Does it clip differently? Do these transistors clip in the 3-5V range, I thought someone said that somewhere. That with the 2N5400 with the collector clipped and the emitter connected together with the base legs as the connection points and I think with the that configuration that would be symmetrical slipping with a 2N5401/5400.


With the same configuration the MPSA06 is asymmetrical clipping I think??????

Thanks for the suggestions!:2thumbsup:
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I tried the Zeners and they are an absolute Brickwall Limiter.. No dynamics pass thru..
Are these Transistors the same way, or so they still have some headroom??
 
midnightlaundry said:
I tried the Zeners and they are an absolute Brickwall Limiter.. No dynamics pass thru..
Are these Transistors the same way, or so they still have some headroom??
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20V/20V will have the most headroom. a transistors wired as a diode clips even more than a higher voltage zener diode. You either like how diode clipping distorts and affects the tone or you don't, that's why alot of people like just adding all tube gain stages to their amps. It's all personal taste kinda thing.

You can put the diodes on a switch to turn them off and on.
 
I snapped a couple of pics today. I am liking the amp way more than I anticipated...........it just rips for only 3 gain stages :p

I removed the JJ's for start up and installed some new 9th generation Ruby Chinese AC5's in V1, V2, V3 and GE6550A's in V4 and V5.
 

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Well gentlemen..... things have devolved. I am getting a thin metallicy distortion and the low end is not full as it should be, it was kind of there on start up but I thought it could be tube related so I swapped tubes for new ones and then I swapped the used GE6550A's for known good EI 6ca7's and the thin metallicy low end is still present and seems to be getting worse. I made the mistake of not testing the output transformer while the amp was totally blown apart. I do remember this amp not sounding it's best before the teardown but I assumed since I knew the original owner there was no way the output transformer was bad. The good news is that the power transformer is 100% healthy.

I've checked all the signal inputs and solder joints via the chop stick testing and nothing is crackling and no solder joints look cold, so I am having to consider the output transformer with how things are behaving and sounding.

Is there a quick and dirty way to pull the power tubes and test the impedance of the output transformer in the amp or do I have to unsolder the taps from the impedance selector? I don't have any signal generators or Oscilloscope so my equipment is limited to DMM and a variac.

So it looks like I am possibly in the market for a new Drake 784-139 output transformer. Who makes a good Drake 784/139 these days. I see Pacific Audio is a newcomer for $162..16 but I have to say I like Heyboer and Mercury Magnetics. It's a total bummer but alot of descriptions of failing Drake 784-139's describe exactly what I am hearing.

https://pacificaudiomagnetics.com/collections/marshall

Heyboer from Amp parts Direct for $127.00
https://shop.amppartsdirect.com/col...tyle-50w-output-4-8-16-apd-8025a-h-by-heyboer
 
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glpg80 said:
Inject a sine wave into the phase inverter. Check the voltage on a scope at the output. What do you see?

You can also pull the power tubes and inject a signal into the input. Follow it through the circuit to the gates of the power tubes.

Check your bias circuit. Have you started poking and pushing on anything? Any knobs that don’t affect it or ones that do?
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Thanks, I'm going to have to find a repair shop that I trust that has a scope and signal generator. Yeah I've been checking poking everything that I can think of especially signal carrying leads that could cause what I am hearing.

It's almost like the signal is collapsing, when I disengage the diodes on the master volume it's just sounds thin on the low end compared to my other amps. I seem to remember this amp being kind of lackluster before I decided to mod it but it's been too long since I heard it. It sounds better( really good actually) when I engage either diode selection but the low end and how it hits still sounds and feels off and I can't quite put my finger on it but it's not right. I found two shops somewhat close and I'll call them and see it they can check out the output transformer and do some basic trouble shooting as I'd like to keep the output if it is still good.
 
Stay the course!
Last week when I was in the zone I lost signal and tried all kinds of things, but it ended up being that my Cord was barely pushed into my Univibe on the floor.. I must have stepped on it and pulled it out.. Fuck..

Check your Coupling Caps for DC Voltage on the Input side of each Stage.. It should be NONE..
 
midnightlaundry said:
Stay the course!
Last week when I was in the zone I lost signal and tried all kinds of things, but it ended up being that my Cord was barely pushed into my Univibe on the floor.. I must have stepped on it and pulled it out.. Fuck..

Check your Coupling Caps for DC Voltage on the Input side of each Stage.. It should be NONE..
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At this point I'm like 90% certain it's an output transformer so much so that I am going to buy one and have it on hand. I found one shop that has all the scopes and signal generators about two hours from me. The mod itself sound great......I'll get the problem sorted out on way or the other. I really only want the guy to say yeah or neigh on the original output transformer as I'd like to be the one to install the new one. If this didn't have the original Drake in it I would have already started the process of pulling it out.:yes:
 
Can you post a clip of the metallic sound you're hearing?
 
But why would your OT be fried??
Is there something you're not telling us?? :p
Are the voltages the same at the Powertube Plates as they were when you 1st got it rockin??
It should be the highest voltages in the amp.. Your Screens should be right behind..
 
midnightlaundry said:
But why would your OT be fried??
Is there something you're not telling us?? :p
Are the voltages the same at the Powertube Plates as they were when you 1st got it rockin??
It should be the highest voltages in the amp.. Your Screens should be right behind..
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No nothing to admit to.... I am completely confident in my work. All the plate voltages are fine I posted what those were in the above posts, amp is running about 470DCV for a B+. all solder joints are nice and bright none look cold and none responded to poking, pushing and tapping with a sharpie since I don't have chopsticks.:LOL: It's not blowing HT fuses, the bias DC voltage is stable, B+ is stable. I have only played this amp briefly after I bought it in 2014 and it didn't sound that great then. I also remember that when the other guitar player brought this amp to band practice many many moons ago it sounded feeble compared to my 79 2203 that's why I didn't have a problem ripping this amp apart to mod it. After buying the amp from him I did find the amp wasn't totally stock so then I attributed it's lackluster performance to this strange mod it had and then I tore the amp down at that point. It could be something else but unfortunately my intuition is usually correct.

We'll see the guy I found has a good reputation for fixing amps that other shops did not. I'll tell the guy what I think it is and the other tech can do his thing and I'll see what he finds. I could upgrade it with a 100 OPT and hardwire the 16 and 8 ohm taps but I'll probably stick with a new 784-139 OPT transformer.

This would be the very first amp that did not operate perfectly that I have built but if it's the output transformer that's having issues then I guess that would still be on me for not checking it out fully prior to starting the build. :p:eek:

I'll let you guys know once I find out what's going on with it.
 
Before I gave up and sent this amp off to another tech I decided to do some tweaking........

I replaced my 1 Meg master volume pot today with a 500K reverse log pot as I wanted to see the difference between the two. The volume now comes on early just like a JCM800 style master when engaging the diodes.......Sweet.................. that is exactly what I was looking for..... Thank you to Jeremy( Mr. Redplated) for the recommendation!:2thumbsup:

ANNNNNNNNNNNNNNND........ After replacing the 1 meg pot bammo....... tons of low end is now there and it doesn't feels squashed or like it's collapsing like before. :unsure:

So I can only surmise that I damaged the carbon tracks when I soldered the ground bar onto the back of the I meg pot with my 60 watt piece of shit Weller solder iron that doesn't seem to regulate temperature well at all. My ground bar also goes across the back of the treble pot as well and I used the same iron. I am going to replace the treble pot tomorrow as well and well see if there is even more improvement.

Oh BTW, I love my new/used Hakko 936 it really works nice but I'm still used to the bigger Radio Shack 30 watt iron conical tip. The Hakko tip is a bit narrow for me. I see a new Hakko FX888D in my future as well.............
 
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harddriver said:
Before I gave up and sent this amp off to another tech I decided to do some tweaking........

I replaced my 1 Meg master volume pot today with a 500K reverse log pot as I wanted to see the difference between the two. The volume now comes on early just like a JCM800 style master when engaging the diodes.......Sweet.................. that is exactly what I was looking for..... Thank you to Jeremy( Mr. Redplated) for the recommendation!:2thumbsup:

ANNNNNNNNNNNNNNND........ After replacing the 1 meg pot bammo....... tons of low end is now there and it doesn't feels squashed or like it's collapsing like before. :unsure:

So I can only surmise that I damaged the carbon tracks when I soldered the ground bar onto the back of the I meg pot with my 60 watt piece of shit Weller solder iron that doesn't seem to regulate temperature well at all. My ground bar also goes across the back of the treble pot as well and I used the same iron. I am going to replace the treble pot tomorrow as well and well see if there is even more improvement.

Oh BTW, I love my new/used Hakko 936 it really works nice but I'm still used to the bigger Radio Shack 30 watt iron conical tip. The Hakko tip is a bit narrow for me. I see a new Hakko FX888D in my future as well.............
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I have a bunch of tips left over from when I had an 888D. If they fit your iron, I can send them to you. I use the FX-100 now.

IMG_8289.jpg
 
Alright final report gentlemen........I replaced the treble pot and was UBER careful not to induce alot of heat over a large area of the pot back. I only put a small blob on the pot back and then used my Hakko at about 725*F to melt to solder around the buss bar as quick as I could.

The rest of the artifacts that I could still hear are totally gone, the lowend is nice and tight and punches deep there is also more clarity to the tone. So final conclusion is both the 1Meg master and 250KL treble pot's were damaged by induced heat.

The gremlins appear to be gone and let that be a lesson to me about inducing heat to pot enclosures.............:unsure::no::rolleyes:

I may try an Orange drop for the V1A coupling cap and swap out the .001uf snubber for an orange drop just to see if there is any difference we'll see....I am going to play it as it sits for a while and it sounds killer.

I would like to get 5 to 10 more negative bias volts from -55 to -60/-65 because some of my Rubys's 6550A's are kind of hot and pull some current....I figured I would use them up since i have a two quads of them on hand.

Thanks for all the suggestions and help, it is mucho appreciated!:2thumbsup:

PS... the only reason why the OPT was not blown is because I ordered a new Heyboer for it yesterday! I guess that means I need to build another 50 watt amp........:LOL:\:D/
 
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