I just checked the Evatco website and they stock a big range of electrolytic caps, I really want to go with all F&T caps as replacements, but some values, like 200uF/500V, I need are currently listed as on "back order", so it looks like I need to wait.
Tried other suppliers for F&T caps? I know it’s nice to try and get all your parts in one go to minimise shipping, but if it’s holding your project up, it’s worth looking around.
Good point, I can't really do any ordering cause I'm broke so I'll have to wait till I can afford the new caps.
F&T are okay caps - there's nothing wrong with Vishay. Sprague the brandname is owned by Vishay - if you cut the new big blue Spragues that llook good for restos apart, you find a small Vishay cap inside. Due to improvements in cap materials modern high voltage caps are small.
The 6X8 is readily available pretty cheap NOS or used. The 6C10 on the other hand, is not readily available. My 83 Superchamp uses it. Last time I bought them, I got a couple of second hand ones for about $85. One is a Du Pont and the other is a GE. 6AC10s fit OK, but the envelope is a bit bigger, and it has a 100% and two 70% gain triodes. That is a 12AX7, with the second two are equal to a 12AT7 set of triodes.
A lot of people convert the compactron socket. It can take a 9 pin and a 7 pin side by side in the same opening. A 6AU6 is a single triode of 100% gain - i.e. it's half a 12AX7 triode. 6AU6s are very plentiful and it's a tiny tube. One of the guys on the tele board made an adaptor that plugs into the compactron 10-pin and fits two 12AX7s giving you a spare triode.
Originally Posted by Dacious
Tubes used in my Non-Reverb Fender Super Twin are as follows:
X6 6L6 Beam-Power Tetrodes (actually Mesa/Boogie brand STR 415 6L6).
X1 12AU7 Twin Triode.
X1 12AT7 Twin Triode.
X1 12AX7 Twin Triode.
X2 7025 Twin Triode (low-noise 12AX7/ECC83).
Update:
Recently I got in contact with a mate of mine who just happens to do amp servicing, he offered to give me some second-hand 16uF/450V and 22uF/500V capacitors he had pulled out of an amp, but were still perfectly good, so I took him up on the offer, he dropped-off the caps in my mailbox a few weeks ago, and I had a look through them and selected a light-grey 22uF/500V Illinois Cap as a suitable replacement for the 16uF/500V cap that had leaked, I soldered it into place on the eyelet board under the doghouse, then put the Super Twin amp back together and gave it a test-out, the amp seems to be working fine with the replacement cap installed, so that'll do fine till I can get a full set of brand-new caps ordered.
A pic of the old and leaky cap:
Notice how there's an obvious bulge next to the cap's + terminal?, basically what happened to cause that was that, for some reason, the electrolyte inside the cap got hot enough to boil, and because the pressure inside the cap got a bit too much the rubber bung sealing the + end of the cap ruptured, letting the electrolyte leak-out, if you see an electrolytic cap with a slight small bulge in it's rubber sealing bung, or in a similar condition to the one in the pic, it needs replacing with a new one asap otherwise it could cause expensive damage to your amp.
Last edited by DrNomis_44; 19-11-2020 at 05:25 PM.
Update:
Looks like I'm going to have to do some more service work on my Super Twin amp sometime next week, reason being is that the amp is really noisy sounding, I can hear some loud crackling noises when I take the amp off standby and turn up both of the volume controls, I tried swapping-out V1, the first 12AX7 Tube in the preamp but it didn't fix the crackly noise, although I did notice that the noise went-away the first time I put the 12AX7 tube I was using as a substitute, I discovered that the absence of crackly noise was due to the substitute 12AX7 not being seated properly in it's socket, but that's actually a very useful clue for pinpointing the cause of the crackly noise, I'll need to look at the schematic for my Super Twin amp.
Just had a quick look at the schematic for my Fender Super Twin amp, and I think I know what's causing the crackly noise, I think the treble tone control pot may either be dirty, or it could need replacing with a new one, I'm going to try spraying all the pots in the amp with some electrical clean and lube spray I recently bought from Jaycar Electronics, if that doesn't fix the crackly noise I may have to order some new replacement pots, I think Evatco may have them in stock.
Last edited by DrNomis_44; 04-02-2023 at 03:36 PM.
Update:
Just did an online order on my account at the Evatco website for two 300pF/500V silver mica caps, there are two 330pF caps in the circuitry associated with V1 in the preamp stage of my Fender Super Twin, one goes from the anode of the first 12AX7 triode gain-stage to ground, the other one connects to one of the lugs on the treble control pot, Evatco didn't have any 330pF/500V silver mica caps in stock, so I decided to go with a couple of 300pF/500V silver micas instead, 30pF is such a small capacitance value that I don't think will make much of a difference to the sound of the amp, considering that the silver micas I ordered have a tolerance of +/- 5% of the marked value, besides, electronic circuits aren't as critical as people might think, you can quite easily substitute the next value up or down with no ill effects.
Taking into account it's tolerance, a 300pF/500V 5% silver mica cap can have an actual measured value ranging anywhere from 285pF to 315pF.
Last edited by DrNomis_44; 09-02-2023 at 02:23 PM.
Update:
Just got back home from picking-up a parcel from my local Australia Post Office, the parcel contains the two 300pF/500V 5% Silver Mica caps i ordered from Evatco, these will be used as replacements for the two original 330pF ceramic caps in the circuitry associated with V1 in the schematic for my Fender Super Twin amp, incidentally, I replaced five carbon comp resistors in my Super Twin amp with some modern 1W 5% Carbon Film types and that seems to have fixed the loud crackly noise I was getting from the amp before, so, most likely either one of the original resistors, or all of them had gone noisy, I did notice that one of them, a 47k/1W 10% carbon comp resistor had drifted out of spec/tolerance, it actually measured about 53k, a 47k/10% carbon comp resistor in a worst-case scenario should measure about 51,700 Ohms on the high side (47,000+10%=51,700) and about 42,300 Ohms (47,000-10%=42,300) on the low side.
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