Fender 75 project....


Senior member
Kinda continued from another thread; amp is a Fender 75, kind of an obscure amp that first came out in '79/80 and I believe is a Paul Rivera design. It was the first Fender amp with switching normal/lead channels, but is all tube to include the pre-amp stage; CB can probably add a lot to that. Came in two models, 2x12 and 1x15, mine's a 15, someone had pulled the original reverb tank out of the amp.

A friend of mine found it in a church thrift store whilst looking for other gear, it was $30 and had the power cord cut off; he called and I had him snag it for me.

The 6L6 power tubes were mis-matched and one was toasted (all preamp 12AT7/7025s original Fender relabel tubes); CB's "Need for Tweed" got me dusting it off (had been sitting for a year and a half. Per CB's suggestion I got a cheap set of Sovtek 7581s before shelling out $$$ for a matched set of NOS 6L6GCs. Replaced the power cord, and ran through all the resistors on the breadboard, which all test out OK; was going to order a complete set of new caps, and the power switch is permanently stuck in the "On" position, but curiousity got the better of me; cleaned all the pots/switches real good, plugged in the old preamp tubes and the Sovtek 7581s, and Holy Shit!!!!!

I've a LOT of amps over the last 34 years, and this for some reason, is the LOUDEST dual 6L6 amp I've ever turned on, it's easily louder than a typical unmodded Twin Reverb... CB - The 7581s have anything to do with that??? Extreme Fender tube crunch on that original Fender 15" speaker, even though it looks light on magnet...

Ordering the caps/new switch/snakeskin tolex today, pix, etc. as work progresses.
I doubt its the Sovtek that makes it so.

The ultralinear output of the amp, high high plate voltage, gets it moving.  All the crunch you get will be from the preamp... the output will have a hard time breaking up, and well.. not be very nice if it does... the downfall of the ultralinear design.

Just a guess, but it "seems" loud, and in fact is loud... there's little loudness difference between a Twin Reverb (80-105watts) and the 40-60 watt two output tube cousins in its family. 

Getcherself some Deft Lacquer at Walmart.  When you pull off the old tolex its gonna leave all sorts of fuzz.  Lacquer the fuzz (brush on) and let it dry for 15 minutes, then sand it off neat as anything.  It'll be ready for retolex then.  Getcherself some contact cement (red can, Weldwood).  Coat the amp and tolex... let sit AT LEAST 15minutes but no more than 30.  Press on.  Once is on... and in place, and allowed to set... its on fer good.  Other glues... take yer chances.
Should add... once you get it going well.... maybe get some REAL 7581s.  Pay a bit of a premium for em, but you'll have a smokin' clean machine.

By the time I get done I'll but a matched NOS 6L6GCs in it, found a couple of sources already. I want to pull the original speaker; you ever try one of those Eminence Red Coat Big Bens? Other 15" suggestions?
Just finished ordering all parts but speaker... I can't believe no one makes Fender blackface amp knobs that are labeled 1-11...
To me, there's not a good 15 guitar speaker out there any more. 

I've tried several Eminence... nada.  The old 15's had a certain retained crispness even though they were bottom heavy.  The new 15's... just not cuttin' it for me.  I'd look at perhaps, a replacement for the JazzKing amp.  You can get that thru a Fender dealer and its a special 15 to sound more like the JBL D130F.... a full rich 15 that sounds great.

Forget the Jensen reissues.  The 12's and 10's and smaller lack bottom, so youi'd think... ok the 15 should be just the ticket, right?  Nada.  Pure mud.  No zip at all. 

I really REALLY suggest you get NOS 7581's and leave the 6L6's alone in that amp.  Yes, it will run on 6L6's.  Yes NOS has its mystique.  BUT you need to quit thinking about your amp as a cool old Fender silverface, blackface... its not.  It is the one of the last of a breed that nearly died.  It has ULTRALINEAR output, and you're gonna waste money on tubes that sound GREAT broken up, that aren't gonna break up in that amp.  Furthermore, the 6L6s will not last as well at the VERY HIGH PLATE VOLTAGEs found there.  The 7581 was made to take over for such applications, and it is, in fact, a better tube for the 75.  Why spend big bucks wearing out 6L6s that are not going to give you what you think they will.  The amp might as well have a solid state output for all the breakup you're gonna get.  It is just not gonna happen in output stages with the way they drive it.  And when you goose it up to seven or eight or ten on the dial, you're gonna say... better back it offf.  Ultralinear output does not sound like we think a tube amp should sound.  The screens are busy tracking the plate voltages... and effecting the output as well, able to draw current through the transformer.  When the plates reach saturation, the screens will have more to give by a long shot ... it just sounds... well it damn near SOUNDS solid state (not quite,but nearly).

However, its a very nice clean amp.  Do it (and yerself and yer wallet) a favor and do the 7581s... trust me on this one.  I've reworked a fairly good number of UL output 135 watt Twin Reverbs (the jazz players delight with D130s in it).  They are the tube to use, and will last next to forever, because they can dissipate that wattage easily and not grunt in the process.  The 6L6 might be on the label, but... they have a hard time doing 50 watts.... let alone 75 in UL mode.
CB - You weren't kidding about the guy at Ampwares taking forever to ship an order, I'm about ready to cancel/try somewhere else.

Put an Eminence Patriot Big Ben in with the 7581s and tested, rocks out LOUD, the original speaker wasn't in great shape.

My buddy that buys/fixes/resells high end tube audio gear is coming to town next week, looking at the schematic he thinks the array of caps in the power amp circuit and parallel resistors needs replacement at a minimum, we'll go through all that next week.

What was the name of that other supplier as alternative to Ampwares?
You can try calling him - he tends to go away for weeks, and just leave stuff hang.  With him its either like next day or next (2) months.

after that... ebay but use caution as always.
If you just need caps - www.mouser.com

You shall use Sprague TVA-Atom capacitors, now owned by Vishey..... and none other.  That is what the amp needs, others will not work well, and / or fail.

Your coupling caps are fine.

Resistors unless noisey, leave alone.  Resistors generally will get thermal noise always, but also get a sort of frying pan sound.  This is from trapped water in them.  Run the amp for a while... the humidity might go away if you have frying pan.  Also tubes, sockets... coupling caps can also do frying pan noise.  So... ya gotta use yer noodle when troubleshooting that.

Refresh my memory... you ordered what from AMPWARES?  All the parts?... if ya want, PM me here, I can maybe help ya (again)
Jerry's bringing caps and other components with him, here's what I ordered from Ampwares 17 July:

CSTS Carling SPST Toggle Switch 1 $3.75 $3.75
4ART2S 4AB3C1B Accutronics Reverb Tank, 2 Spring 1 $29.95 $29.95
RLBSWBWARJFTR Reverb Leads, Blackface style w/ braided wire and RCA jacks, fits TWIN/PRO REVERB 1 $31.00 $31.00
SBWT5WPPY Snakeskin Black & White Tolex, 54" Wide, Price Per Yard 2 $14.95 $29.90

When I called him a couple of weeks ago he said he had been waiting on the reverb leads but had got them in and was "shipping tomorrow"; he hasn;t answered his phone all last week and of course mailbox is full. Not anything there I desperately need other than the switch, but just another pain in the ass I could live without...
They look like the pointy toed rhythm tappers John Lee was wearing..... no clodhoppers there!
Ampware order FINALLY came; the snakeskin tolex looks better than I expected, it was hard to tell from the little swatch/pic on the website, but it was cheap enough that if it didn't work I'd exchange it back for tweed or something else, will definitely go with this :

That is gonna be one rude bastid of an amp when you get done with it...

And for the grille?  Gold grille?
Jerry was here this week and checked the chassis; needs a couple of additional components he's going to send I'll get in a a couple of weeks, I had to go into the office and think he tweaked the bias on the 7581s, sounds great had already installed Eminence Patriot Big Ben 15".

The original grill cover is in great shape, but now that you mention it... Where can I get a gold plated Fender amp logo? White sidewall caster wheels, maybe better yet caster wheels with little gold "rims"?

Guess I'm going to have to forget CB's gold suggestion, because the only "mag/rim" replacement casters I can find only come in chrome: