Tube Amp Archive

The Ampeg logo plate and bulbs arrived from Fliptops.net a couple days ago. I got them installed tonight.

Thanks for the link. The papers are both very informative and often a hoot to read. Like ... * Be sure to turn the power off to the amplifier before discharging the electrolytic filter capacitors, or you will get an unpleasant surprise. * Be sure to remove any capacitor-discharging jumper wires befo...

Just got a pair of 7868s from TubeWorld ... I suppose one should put them in simply to test operation?

Yes, it's posted in earlier posts of this thread. The early SB-12, with 7868 tubes. Prior to the later builds, with 6L6 tubes. And there's a picture of the undersides showing the entire layout of parts. There were comments that the paper covered caps and the blue ones should be replaced, but probabl...

Going through the caps again. So the big one, 30uF 600V seems easy enough ... like the Miec one ... it's an axial, does that work? And the 20uF 450V electrolytic ... axial or radial, either? Next ... the 2x 20uF 450V ... Miec has a can type 20uF + 20uF, for $14.99 ... that would be the correct one? ...

I love the helpful information given here!

Thanks ...

Neil

I'm ordering those replacement caps for the three big paper wrapped ones, and the blue ones, as suggested. So sometime over the next month or so those will get swapped out. I'm also simply ordering that pair of old style 7868s. I'm curious as to what difference if any, in tone or timbre might occur ...

Wow, that's a great link! Thanks for posting ... I'll be ordering from them I think.

I've never seen a 2x capacitor ... two leads on one end, on on the other, before ... that's an interesting thing.

Very helpful information and it seems, rather pracitcal advice.

Thank you kind sirs!

Ok ... it would be $130 plus shipping for the pair of RCA 7868's from TubeWorld. Add in a pair of AX7s, and the 5AR4, that's going to be well north of $175 to get a replacement set. A pair of JJ 7591's on the other hand is around $65 plus shipping. Would be probably around $100 for the complete repl...

And Brendan from TubeWorld (in Wisconsin) says yes, he has a matched set of RCA 7868 tubes in stock. Maybe I'll order those and consider a socket swap at a later date ...

Neil

So this would be the modern replacement for the big brown 30MFD 600v cap?

https://www.studioelectronics.biz/sunsh ... ail&p=1586


Neil

Thank you, you are being most helpful! The gray thing, so it's the first of the power resistors. Great ... um ... so, what value is it, and how would one know what to replace it with? I take it a first order of business is to replace the large brown paper caps, and above it was recommended to do the...

And I'm curious what the brown multi-pin thing is mounted to the treble/bass pots is? Looks to have something like 6 pins ... and that gray tubular thing?

I'm trying to sort out cap types, too ... the yellow ones are ... what? The blue ones ... what? The brown paper wrapped ... what?

The really fun thing for reading schematics ... they don't show actually anything in "real" locations! So I have to try to read the data off the item, hoping I can move it so I can actually see all the relevant data, and then look up on the schematic to see if there's something mostly like that list...