Lectrolab 300

[monsteranus]

Stumbled across this rascal recently. The intial check out had a nasty low volume output. I swapped out the preamp and output tubes with some I had on hand to get rid of the nasty but still had a volume issue. I replaced the coupling cap between the first and second stage of the preamp tube to restore the volume. Now I hear a hissing much like how an old radio would have static between stations. I replaced the electrolytics at the cathode connections as well.

It still has the two prong power cord I plan to change out. One odd thing I see is the values on several parts dont match the parts list values on the schematic.

Whats the best type cap to replace the old tubular paper condensers with?

The main filter caps are in a single can style, are these electrolytics as well?

The preamp is a 6SN7, the output is a 6V6.

[monsteranus]

There was no noise when I was only getting volume at about 1/3 rotaion of the volume control, very clean sound.

[Jazz P Bass]

Can you isolate the hiss to a particular circuit.
The cap that you changed "may" be bad.

[monsteranus]

I used an orange drop I had on hand. I also changed the cap coming off the tone control with an orange drop. The hiss increases with the tone control. When the tone is all the way down the hiss is still there, just very muted.

It has a disc cap connecting the pre out to the input for the power tube. I can contact the pre side of the cap with meter lead to hear a crackle noise.

[monsteranus]

I have replaced these parts, C2, C5,C6, C7, C8, R4 and R7

C5 and C8 had 10 MFD @ 150 volt electrolytics where the schematic shows 50MFD @ 15 volt. I put a new 10MFD @ 250 volt I had on hand @ C5 and C8 but later I put a 50 MFD on the preamp tube. The noise was present before and after. Could it be the 10MFD still on the power tube?