"Newbee" w/ Twin reverb question....

[TubeJunky5]

Just signed up. Looks like a fantastic forum!
Please give me a little slack here...I just got my first Twin and it's the
first Fender I ever decided to try to"tweak".

Unfortunately, I probably can't afford a vintage "black" so I got this
1980 Twin. I have discovered the Bias circuit is the dumbest thing
I've ever seen. I can't figure how to get rid of all that s*** yet!

I did change the PI to the "black" values, so I'm gettin' there.

Sorry. Anyway, I bought a filter cap "kit" for it.
the factory mallory's were two 220mfd--three 20mfd and 20 70mfd caps. In the kit I got the 220's....20's and 100's--??

would you guys recommend switching out the 70's for 100 caps??

Thank you

[TubeJunky5]

hey, never mind!

I just read the 70mfd cap is not made anymore.

the 100 is the standard replacement

[steve25]

Hi, to fully get the 60s BF tone out of that 135 watt amp several more things need to be done, and it can be a fun skill building project!
1) The power transformer needs to be changed out to something like Mojotone 763 model whicj will bring the power supply voltage down to the 460 range form its now 500 volt.
2) A choke like Mojotones model 777 needs to be installed also, if you go to the Fender amp feild guide site you can find the schematic for your amp and the needed 1960s AB763 schematic.
3) Since your amp has a ultralinear output transformer you will need to unhook the screen taps and once again rewire and add the parts to match the AB763 model.
4) You will per the AB763 need to rewire the bias circuit to match.
5) and maybe most important, change out the amps current speakers ( most likly Eminence made) for Jensen model C12N models. Now you have atleast 90% Blackface tone and feel!

[Kap'n]

That's a lot of work for a butt-jointed, 'chocolate-dropped", plastic-coated-stranded-wired rats nest of an amp.

I'd maybe require the the phase inverter and the bias scheme. If I didn't like that, I'd flip it some something I liked better.

[phantomman]

That's a lot of work for a butt-jointed, 'chocolate-dropped", plastic-coated-stranded-wired rats nest of an amp.

I concur, Kap'n.

At least on a HRDlx refurb (like TJ does) the cab, chassis, an' iron git "recycled". On a deal like this it all hasta go. 'Bout that only thangs reusable will be the chassis, knobs, an' control panel(s).

"And that's a helluva price to pay for bein' "stylish"!"

Jus' mah 'pinion, y'unnerstan'......

[Kap'n]

TubeJunky5, I didn't mean to denigrate your amp in any way. It is what it is, a SF ultralinear twin. The couple modifications I mention warm it up. If those modifications don't have it sounding to your taste, you have the wrong amp, and should find another.

Steve25 is suggesting massive, expensive modifications, that require things like drilling holes in the chassis. Those modifications would make it almost like an earlier SF twin, only it would cost more, and completely destroy any resale value it might have.

[TubeJunky5]

Oh, no problem! I already hate the thing!!

I did about 90% of the BF changes...plus fixed the power tube
filament polarity prob. New filtr. caps made a HUGE difference!!
It's a much better amp. Fortunately, it does have the Jensens.

Changed the board caps to Jupitors and replaced the electlt. caps too.
I doubt I'll do much else....too much hassle.

Bad part is....now the rvrb is not working! The pots are fine,wiring and solder joints seem solid...tubes are ok.
I've read how to check continuity of the rvrb tank w/ my meter.

Can anyone suggest anything else to inspect/check????
Kinda lost at the moment!!

[boobtube21]

Can't help with the reverb as I'm not much of a tech, sorry...

But I will mention that I was going to have my tech rewire my bias circuit, but he said he got decent bias voltage out of it. Being the suspicous wanker I am I pulled the chassis and checked it myself, and it was fine. So in case you haven't done the bias revamp yet, you might want to check your bias readings it first and see if it even needs it.

On top of that good speakers make a huge difference, but I see you've already got some Jensens in there so you should be good to go.

[Kap'n]

Does the tank make sound if you shake it?

[Gris]

Yeah, the larger transformers are expensive. Swapping them both could get really costly!

[TubeJunky5]

Does the tank make sound if you shake it?

please forgive my ignorance...this is my first rvrb amp.
what "kind" of noise are we talkin' about?
i took it out of the vinyl cover and opend it up....it appeared ok...
but i don't know a damn thing about revrb tanks!

[TubeJunky5]

Yeah, the larger transformers are expensive. Swapping them both could get really costly!

sheewww.....an OT from MM is $280 ! I didn't even look for the

PT price!! That's a big chunk of iron!!

.....done w/ the modding on this one!

[Kap'n]

Sorry, I meant if the amp is on, and you shake the reverb tank, does it make a big crashing sound through the speakers?

[phantomman]

Sorry, does it make a big crashing sound through the speakers?

Ayup......like Dick Dale, havin' a bad hair day.

When performing this "shake" test, best that the amp's volume ain' set too high.

[TubeJunky5]

Sorry, I meant if the amp is on, and you shake the reverb tank, does it make a big crashing sound through the speakers?

Ok! I'll try that this week.....it's down at my buddy's home.
I think I can get down there thurs.

Obviously, the "crashing" sound is not good, huh?

if that's the case....R and R would be the path of least resistance??

[phantomman]

No......"crashing" means that the reverb tank is in fact passing a signal and that the recovery circuit is operating.

HTH

[Kap'n]

[quote=phantomman;496950
When performing this "shake" test, best that the amp's volume ain' set too high.[/quote]

Actually, the "Reverb" level. It's independent of the amp volume controls, unless it's got a master.

[phantomman]

He did indicate it was a 1980 model. I'm pretty certain that it's MV-equipped.

[TubeJunky5]

yes, i kept the MV in place.

gotcha! I'll check for the "crash" this week......

thanks for everyone's help thus far!!