Help me identify circuit

[hebaton]

I have a silver face Fender Dual Showman reverb. ( I am told a 1970 )
I cannot find the circuit number anywhere, and There is a sticker on the back saying serial number : 2070 which does not seem to be a fender SN
Here are pics of what I tout relevant.

Your help would be vey much appreciaed.
Also, I hear and read of "black facing" silver face amps, Is there i guide to doing this I could provide my tech with ?

Thank you all !

[Stevem]

By those numbers on your transformer, yes your amp was born in 1970.

If you go to the Fender amp field guide site go to the listing for a twin reverb.
Click on the black face one.
Next scroll to the bottom and click on chassis layout.

This will open up a factory drawing of how the amp was wired.

The twin reverb and the duel showman reverb where the same amp in all respects relative to there era, but for the silver face bias circuit they started using on later models ( bias balance) and the hum balance pot and name on the faceplate!

A silver face Super reverb wound be the same amp, but minus 2 output tubes and of course smaller transformers.

As you go into the mid 1970s silverface amps they no longer used a choke, but a resistor and the output stage was UL.

[Stevem]

Here’s a gut shot of my black face Bandmaster.

This shows how some of the many Cost where cut on CBS era amps.
Notice how the wires on my amp where twisted to help stop interaction and oscillation issues and on yours they are just run straight with that purple ground wire somewhat rapped around then to try and shield them.

The reason CBS did this was to save on wire cost. Because it takes more length of wire if it’s twisted to get from point A to point B.

[hebaton]

TO me it looks like the layout in my amp is the AA270 ( if I look at the Bias circuit )
Is this the "balance" rather than bias adjustment ?

IS there a good reason to make some changes in this amp, and if so, Is there a step by step guide I could give my tech so he knows what needs done ?

[hebaton]

I found this post on another Forum :
" Hello All. I have a 1970 Twin Reverb (AA270) and have modified the PS resistors to BF (4.7 k etc.) for higher supply voltages. I have also installed two bias pots to replace the balance bias pot. I removed the 2000 pF snubbing capacitors on the power tubes and have had no stability issues."

Would these simple changes make a significant difference ?

[Stevem]

Why don’t you get the amp in good stock working order and play it for a few weeks to see how it pleases or displeasures you and then make a list of what you might want different.

Don’t take this the wrong way, but some peoples taste and musical sophistication levels are easier to please then others and you may just find that the amp puts a smile on your face in good operating stock form!

In my mind the mod I would do first to these silverface amps once there working good is to junk those stock orange label Utah brand speakers because by that era they sucked!!

PS.
By the way you should not have to provide a good experienced tube amp tech with instructions on how to do common mod’s and up grades to these plentiful old amps.

[Ten Over]

TO me it looks like the layout in my amp is the AA270 ( if I look at the Bias circuit )
Is this the "balance" rather than bias adjustment ?

The bias circuit has been altered by someone who didn't solder very well. In light of this, my money is going on AA769.

The original bias balance has been modded to bias level using the classic one-wire mod.