Replacing LDRs in Studio Preamp

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synaesthesia

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Replaced the two 21L883 LDRs that control the channel switching. The Preamp was sputtering audio signal on channel switching and distorting in the clean channel due to leaky LDRs. The replacements are VTL5C1, but the cathode is on the other side on the VTL5C1, see pics, they are where the notches are on the shells of the LDR. Clipped off the old ones, soldered the new ones (upside down - viz. print side facing PCB so that the cathode lines up with the the replaced 21L883's + side). A bit tricky but managed to solder on to the stumps, did not bother to desolder the LDRs, too much of a job.

The preamp is now right as rain. I can raise my gain in the clean channel and play with humbuckers and still get a clean tone, and it is a bit louder too (my LDRs should have been replaced long ago haha!) The switching is smooth, sputtering is all gone and I am a happy camper. Sorry the pics are on an external website, I couldn't find how to upload images here.
 
Hey, thanks for posting your work. I just purchased a Studio Pre last week and I'm looking to have it refurb to it's orig glory! This was something I had no clue about. Will mention this to the amp tech during refurb.

Are there any other particulars that you would recommend for the Studio Pre that would make this amp last another 30 years. It sounds pretty good now, but I am betting it can sound better with a little TLC. I'm planning a cap refresh, reverb tank replcmt, tube replacmt, and perhaps the fix you applied above. May I ask, which preamp tubes you suggest? I prefer a high gain sound, with decent bottom end as well. I like the JJ, but I'm always open to suggestions from guys who actually have tested, tried and true experience with particular amps/tubes.

Once again, thanks for your post
 
Leave it if you want high gain but if you want assurance of more clean headroom the second tube could be a 5751.
 

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