Marshall 4010 cap. question.

[Garydean]

I'm replacing the orange drops in this 20 year old JCM 800, 4010 1x12 combo. I replaced the filter caps as well as a few resistors in the first stage of the preamp, a few weeks ago. In this picture you can see a red block style cap at the edge of the board labeled. .68 100-. I have a .68uf 630vdc metal film, tubular cap handy to put in it's place, is this OK?. I have some DC leakage in this stage, so I figure while I'm in there I should replace everything.

My question is, the amp needs to be tamed a bit as the highs are piercing. I assume the red block cap is a bypass cap? By changing it's value, would this also have an effect on sound quality or tone? I had heard by changing C-5's value (ceramic) or removing it would also tame it a bit.... any thoughts there?

thank you,
Gary

[drewl]

The .68 is the Cathode cap of V1.
There's only a few volts across it, so you don't need a large rating.
You can experiment with the value of the cap to change the sound of the amp.
It should be in parallel with a 2.7k resistor. this is the bright channel on standard non master amps, the normal channel has a 330uf in parallel with an 820 ohm resistor which shows how wide the values can be.

[dai h.]

why would you need to replace that cap? I would guess typically it will probably never need replacing. When you say "DC leakage" is this referring to the voltage at one end of this cap?

[Garydean]

thanks! I do have a .33/250v lemon drop I could put in. How would that change the sound rather than kicking it up to a 1. lemon drop?

G-

[Garydean]

Sorry, I posted before I saw your reply. I'm getting a buzz, not hum, in the preamp first stage. I can't remember my readings, but it lead me to believe the original orange drops were leaking a bit. I figured I would replace those and this cap as well. Overkill?

thanks for your reply,

[Enzo]

It is pretty unlikely the cathode cap there is leaking, and it would not add buzz or hum if it was.

I'd worry about a 20 year old tube there first.

[Garydean]

Thanks guys, I've swapped out the preamp tubes with about 5 different new and nos ax7's. I think I will leave the cathode cap in as per your advice, and just replace the Orange Drops.

[Garydean]

I finally got the amp to perform 100% with little if any noise. Most of the buzzing was due to wire placement in the preamp section. The grid wires needed to be away from the chassis and all other wires needed to be against the chassis. I reworked questionable components as well.

Just thought I would report my results, in case some one ever has this problem with their 4010.

Cheers