Fender Amps

Tweed era 5F8A build. Presence circuit bad design!

feeds@yuku.com (Fenderonly) — Sun, 06 Dec 2009 15:34:23 GMT

The presence circuit of the high 5F8A (high power tweed Twin) allows around 12VDC on the 5K presence pot. Makes for a scratchy pot.

Any thoughts on improving that? Perhaps a 22 to 25uf tantalum cap in series with the pot leg to decouple the DC and hopefully still pass enough low end thru the pot to ground?
I have had a lot of success with using tantalum caps in place of electroytics between the gain stages in the Peavey Nashville 400 steel amp mods I have done. They have...

BXR Spectrum Cabinet

feeds@yuku.com (jbmojo) — Sun, 29 Nov 2009 07:39:27 GMT

I need to replace the 2x10's in a BXR Spectrum cabinet (2x10,1x18). Anyone know what Fender used in there? I'm pretty sure they were 8 ohm but got no idea on the power rating...and no old speakers either.

A Tale of Two Chokes

feeds@yuku.com (SG123) — Fri, 30 Oct 2009 19:52:03 GMT

Weber sells part #W014684 that is described as "Choke for Tweed Fenders" 5-8 Hy. 200ma. 125 Ohm.

They also have W022699 which is more or less a Fender 125C1A [ 022699 new part # ] equivalent
9 Hy. 120ma. which is about half the price [ and half the size/weight ].

Both have #22AWG. leads.

Is the larger choke overkill, or is there something unique that makes it "better" for tweed Fender applications? I've seen original tweed '59...

Hot Rod DeVille Mods

feeds@yuku.com (jbmojo) — Wed, 21 Oct 2009 18:15:43 GMT

Aside from the plate resistors, what other parts should I change on one of these to keep 'em from burning something else up?

Twin Reverb II deep sixed in flood

feeds@yuku.com (vox007) — Mon, 28 Sep 2009 20:26:04 GMT

A friends TR II was completely submerged in a flood last week. I have taken it apart to dry out,sprayed the pots,tube sockets & jacks. The speakers look ok ,but I'm sure they're toast. After I know everything is totally dry & clean,should I plug er'in and take cover? Any advice at this point would be helpful-----Ron

A new one for me.. PR

feeds@yuku.com (Andy ZZ) — Thu, 03 Sep 2009 16:10:08 GMT

I have a minty BF PR on the bench with the follwing issue:
At low volumes, fuzz accompanies the signal.
At mid volumes, the fuzz is more or less gone, but the amp is VERY sensitive to buzz from pickups, and noise from volume pots on source guitars.
At high volumes, the tone sounds almost normal, but the pickup buzz is almost overpowering the guitar's tone.

This sounds like early preamp stage to me.
I wont get a chance to look till the weekend. I'll have...

Boogied and Boogered Princeton Amp

feeds@yuku.com (retrorod) — Wed, 26 Aug 2009 21:19:39 GMT

Thought maybe someone would enjoy this story of my latest find and project. While picking up a Hot Rod Deluxe repair job from the house of the local Blues Icon, I was scoping out the garage containing a bunch of his musical artifacts. My eyes landed on a little brown amp against the wall under a table. It screamed brown-face Fender. Curious, I inquired and he told me to pull it out and look. Sure enough, brown Princeton with a big ugly 12 in speaker mounted loosely with 3 screws. He proceeded...

1975 Super Reverb making a strange noise

feeds@yuku.com (altercreed5150) — Tue, 18 Aug 2009 21:34:00 GMT

Hey guys, i have a 75 super reverb that has recently had new caps installed, tube sockets replaced, all resistors on the tube circuit new, new bias caps, pretty much everything has been replaced on this amp...it was in bad shape when i got it...the bias voltage is running about -49vdc, and 43mA on the 6L6 tubes...my problem is that when i play through the amp, it sounds as if the speakers are blown...i have ran this through another cabinet and still...

DC on the tagboard

feeds@yuku.com (RussBert) — Sat, 01 Aug 2009 21:16:04 GMT

I've read about this in Gerald Weber's book, but this is the first time I've seen it.

The amp is a '68 drip-edge Bassman. The symtoms are scratchy volume pots. I read DC (about 3 volts) on both volume pots.

I read from 4 to 5 volts DC where the B+ connects, to about .4 vdc at the input side of the board. I read about -.2 volts at the bias feed resistors. Short of replacing the whole tagboard board, I rekon there ain't much I can do...?

Any of...

Fender Princetons 1964 , How do I deal with high B+ voltage (and screen voltages)

feeds@yuku.com (nigelwackenfrets) — Thu, 30 Jul 2009 14:13:36 GMT

Hi amp gurus: I have two princetons that were produced in May 1964, supposedly to the 6G2 circuit. One has the original PT and the other has just had a Weber replacement PT installed. Here is a pic of the first resistor down from the B+ voltage (first amp had a 10K/2watt resistor from Fender).

here is the second amp, configured like the original Fender:

Adding a headphone jack to a classic (AB763) output stage.

feeds@yuku.com (MadDave12) — Fri, 10 Jul 2009 14:44:44 GMT

I'm looking for a schematic or guidance on adding a switching headphone jack to an output stage similar to that in an AB763 design.

Is it as simple as switching to a 50W 4-ohm resistor, and putting the headphone jack in parallel? Maybe with a dropping resistor to limit the voltage seen by the headphone?

recaping a 72 super reverb

feeds@yuku.com (altercreed5150) — Mon, 18 May 2009 16:03:22 GMT

will it hurt the amp if i use 80uF caps instead of 70uF caps?

Custom Vibrolux Reverb

feeds@yuku.com (StoSoStu) — Wed, 13 May 2009 19:09:39 GMT

I have one on the bench that came in for a check after it had suffered a voltage spike on the mains (lightning I think). Anyway it all checks out and I fixed a couple of little faults but this thing hums like a bugger, with all the controls at 0, and with no input, if I turn up either volume or the reverb I get a hiss on top of that. It seems to be coming from the summing point of the two channels and the reverb return, pin 7 of V4. I had a quick Google and it appears that these are a...

PA100 conversion to a decent guitar amp

feeds@yuku.com (Fenderonly) — Wed, 13 May 2009 13:04:29 GMT

I took one of these in on trade this week in trade for work done on a 1968 Vibrolux.

I decided to do the 2 channels to the Fender standard tone stack with the 6.8K to ground for the mids. The difference in the first channel and the others is now night and day. This thing sounds like a lot more like a Twin Reverb now!!

The other changes to make the power section like a Twin will be small. I have to change the .022uf caps to .1uf caps on the plates of...

Hot Rod DeVille Noise

feeds@yuku.com (jbmojo) — Tue, 28 Apr 2009 12:31:41 GMT

Why would I get a couple of quick pops when the standby switch is thrown on? Got a HR DeVille doing that when I kick it on. Nothing else happens after that, just when the standby switch is turned on. Everything else is fine with it. Filter caps maybe?

Ha Ha Hot Rod DeVille

feeds@yuku.com (jbmojo) — Thu, 16 Apr 2009 02:19:58 GMT

You ain't gonna believe this one.

I posted a topic on Tech Bench about reverb tank ID's, but this really has to have it's own topic.

The HR Deville I was referring to on the TB forum does indeed have a serious problem with the reverb circuit (this is killing me trying to type while laughing so...

How to bias a SF princeton?

feeds@yuku.com (Nicknirk) — Wed, 15 Apr 2009 12:44:03 GMT

I have a 77 SF princeton I just got off of ebay. It has no speaker and no tubes. I got it to start learning to repair tube amps. I have since ordered a Weber 10150T and JJ6v6's and all the rest of the tubes to fill out the set. I'm hoping to try my first bias adjustment on this amp. It looks like someone has installed an adjustable bias pot coming out of the extension speaker jack. How do I adjust the bias on this style of amp the old fashioned way? and how can I check to see if this...

What the #%$&?

feeds@yuku.com (spoony) — Tue, 24 Mar 2009 14:36:19 GMT

Thought you guys might find this amusing. For those of you who already know whats going on in this picture don't say anything maybe we can get a few good laughs at the guesses.

Regards,

Spoony

Question with Princeton Rev PI circuit

feeds@yuku.com (mxvin) — Fri, 13 Mar 2009 22:02:17 GMT

Hey Guys.....me again

First let me apologize that I don't know the proper names of the parts of the circuit of the PI. So my description lacks some logistical finesse....

As some of you know I have just fixed the hum issue with this amp via new...

Maintaining vintage value........68 Princeton Reverb

feeds@yuku.com (mxvin) — Wed, 11 Mar 2009 18:50:00 GMT

Hey Guys,
Some of you have helped me solve an issue with my 68 Princeton Rev. I installed aWeber cap can to fix the problem.
My question is:
The Weber can is small enough to fit into the original Mallory can if I gut it. Ethstectically it will appear stock.......is this a big issue? Of course if I sell the amp I will be up front with the cap replacement. Just wondering what you guys may think about this.
Thanks