Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 335rat on June 28, 2019, 02:44:15 pm
-
Hi!
I have an old Fender Super 60 that I mostly use for the clean tone. I'm quite happy with the tone but got interested in if I could do som mod to it. When I looked at the schematic I saw that maybe it would be possible in an easy way to convert the preamp to the AB763 cirquit and get rid of the overdrive section. Now I have done that mod but it does not work and I have some kind of crackling loud noise when I turn it on. I have studied the schematic over and over again but can't find what's missing and I'm afraid to turn on the amplifire again because of that noise.
Are there maybe someone here who can help me and tell me what I have done wrong? I think I must have missed some important thing in the schema. I have marked in the attached shematic where I made the changes so you can see it.
Is it possible to drive the amplifire without damage without the output tubes and listen just at the ”pre amp out” connection so i don't get that loud noise to the speaker?
-
I have done that mod but it does not work
I would "undo this" 1st - putt it back to original, then when it works.......
If you know what you're doing you can ground the input signal to the PI - BUT I did n't look at your PA section, so wait for a 2nd or verify
-
on 2nd
hit thought.... did your change the preamp phase with your mod?
because of that noise.
-
V102A has no grid to ground resistor. Not happy.
-
The mod you propose would be a real challenge even for an experienced technician. The pcb further complicates this mod.
Look in Hoffman's schematic library. There is a text file describing some simpler mods that may interest you. This all assumes you can undo your non-working mod and get the amp back to original operating condition.
-
Thanks for your quick replies!
And thanks PRR for checking my mod because as you expected it was the lost grid leak resistor that was the problem. I also had to reverse the outer lugs of the volume pot to get it right. After a short test I think it works and it seems to be very loud with the 6L6 in the poweramp. Have to test it more tomorrow and hope it will turn out well.
My intention was only to change the preamp to see what happens.
I'm sorry but I can't find the textfile with the simple mods you suggested Sluckey. Othe mods I've found are only on the overdrive channel.
Here's an updated version of the mod. Oh I also changed the tonecap C4 to 250pf as in the blackface tonestack.
-
https://el34world.com/charts/Schematics/files/Fender/Fender_super_60_mods.txt
-
Thank you. I've seen those mods on a lot of sites and I think they comes from Premier Guitar magazine and they say it's most for the overdrive sond.