[Icedsounds]

I am wondering if I could get some help modifying my Jolida amp. There seems to be a tonne of info about the 302/502 but not much of anything for the 801.
The amp I have is about 12 years old and I figure its time to recap the P/S electrolitic caps and start doing some upgrades while I am in there. Right now my amp sounds like an earfull of mashed potatos. There is no channel seperation and all bandwidths sound nice and scrunched and blended together.
As far as the mods I have planned I am going to change signal caps to boutique caps, do the signal resistors, change the volume pot, get rid of the selector switch, change PS caps, bypass PS caps, change signal wire to better stuff, And clean up some of the solder.
I have a couple of burned resistors on one of the boards. I willl replace those but would like to know what would cause this, and if a differnt value can be used to stop this probem. As for my questions

1. What volume pot resistance does the 801 use? (is it 50k ar 100k) I know the 502 has a 50k but it also has a 50k ballance circut that the 801 does not have.
2. Can I replace the stock 470uf 450 volt caps with 500uf 500volt without any adverse side effects? These are before the power supply board.
3. Does anyone know what number the grid stop resistors are on the pcb or schematic? I do have my own schematic but I dont know if it would be appreciated if I post it online.
4. Can I put bypass caps on the power supply caps by just soldering on the backside of the pcb?

Pic of burn resistors



Pic of 470uf caps



Internal pic of amp (for those that havn't seen one. I couldn't find any on the net)

[NagysAudio]

1.) Should be written on the back of the pot, or definitely in the schematic.
2.) Yes, these are power filter caps, they can be 10,000 uF if you want.
3.) Values should be listed in the schematic, also they are written on resistors sometimes, if not then they are color coded and the color code chart is readily available online.
4.) Those caps are already bypassed, no need to bypass them yet again. The bypass caps are usually located on the circuit board itself, close to the tubes, or transistors if it's a solid state amp.

[Bill Baker]

Hi Icedsounds
 The 801 you have is a very old version. Looks like second generation. You will propably not find a schematic for this model anywhere and it has a different circuit as compared to any of the later version. Unless you are sure your schematic is for this older model, it will do you no good.

 To answer some of your questions:

 Power supply caps: You can go with 500uF with no problem. I would recommend bypassing these as well with a good film cap. I would solder them directly to the PS caps rather than the board.

 For a volume control pot, 50K or 100K would work just fine. Probably has a 100K in it now.

 The resistors shown that are showing signs of burning are probably fine. They obviously do get pretty hot and it would be a good idea to replace them. I would use 5W Dale CW wirewound resistors here.

 For grid stop resistors, you will have to follow the wire back from the tube socket. If you are going to replace these, I would recommend soldering the resistor directly to the tube socket and run the wrire from the resistor back tothe appropriate spot on the board.

Replacing those silicon diodes will also make a difference

[NagysAudio]

Bill,

Any reason why you recommend soldering the bypass caps directly to the filter caps? Usually they are located as close to the tubes, or transistors as possible. Especially the input stage. This should reduce noise. But I suppose for a tube amp it's not that critical...

[Bill Baker]

Any reason why you recommend soldering the bypass caps directly to the filter caps?

Yes, you are correct. You caught me on that one. You do want the bypass cap(s) as close as possible to the 'device' that part of the circuit is feeding.

 I cannot tell from the pictures if there are bypass caps already installed for the filter caps.

[Icedsounds]

Thanks for the help guys.
I do have a schematic for the old sj801. I know its an old model but it should have some potential.
I pulled out the volume pot and to my suprise it is a 10k piece. Too bad I have a few nice 100k volume controls laying around I would have liked to use.
Today I replaced the 470uf caps with jj 500uf 500volt caps and bypassed them at the terminals with a couple mundorf zn 0.1uf caps. Hooked the amp back up for a listen. I was quite amazed at the difference I could hear already. There was more sparkle in the top end but the bass was Much better. It changes from one muddy note back to a wide range of music that blended into the mids much nicer.
I changed the selector switch over to a dact switch I had sitting on the shelf. I dont know how much improvement it added to the sound but its expensive so it MUST make it sound better.
I got some mundorf silver oils sitting here waiting to go in then after the burn in im going to change over some resistors and diodes.

[Icedsounds]

The new caps were a bit tricky to get to fit. they are twice as long as the old ones. I ended up using new clamps and mounting them to the side panel.
Heres a couple pics




And soldered up with the bypass caps

[Icedsounds]

I am looking at replacing the diodes. I have some 1200 volt 8a hexfreds. Would I be able to use these or should I get some new ones.