Fender Twin Reverb

[Big chief]

Silverface believe to be 1975 with master volume low volume
Have replaced power tubes and pre amp tubes
Voltage V1 pin1 210 pin6 213 V2 pin1 209 pin6 208 V3 pin1 400 V4 pin1 150 pin6 150
V5 pin1 338 pin 6 337 V6 pin 1 300 pin6 287 V 7-8-9-10 pin 3 429 pin6 424

With volume pots at full open very little sound have used 2 different speaker cabinets 4 ohm
Any help would be great. Thanks

[shooter]

got a scope?
what's the bias VDC on the grids of the PA tubes?
does the amp have a "pre-amp out" jack? 
If so, can you feed that out into another amp/mp3 player?

[pdf64]

Does the issue affect both channels?
What’s the V6 cathode voltage, pin3&8?

[Latole]

What is the heater voltage at each tube ?

Any mod in the amp ?

[uki]

If you could provide the schematic it would be a great help.

[sluckey]

Contact plexi50. He does a lot of repair work in your area.

[Big chief]

Grids V1 pin 2 0 pin7 .03 V2 pin2 0 pin7 .03 V3 pin2 0 pin7 .06 V4 pin2 0 pin 7 .02
V5 pin2 12.9 pin7 12.2 V6 pin2 82 pin7 76
V7 pin8 0 pin3 424 V8 pin8 0 pin3 425 V9 pin8 0 pin3 429  V10 pin8 0 pin3 429

FYI plex is a good friend and helps me

[Big chief]

I do not have a scope  no amp out jack
I’m retired and love to work on old amps as I have played old country music for 71 years

Thanks

[Latole]

https://ampwares.com/amplifiers/fender-silverface-twin-reverb/#

Yesterday ; where is the answer ?
What is the heater voltage at each tube ?
Any mod in the amp ?

[Latole]

You need a scope and signal generator ; A basic tool to work in a amps.

Without these tools you will only be able to fix the easy problems.

If you don't have these basic tools, you have to compensate with a solid knowledge in electronics

[Big chief]

I have a fair knowledge of tube amps I mostly do the easy stuff

Heater voltages V1 2.3 V2 2.3 V3 3.0 V4 2.3 V5 3.0 V6 3.0
 V7 3.5 V8 3.5 V9 3.1 V10 3.5

Does not appear to have any mods  this amp has been mistreated imo
I’m trying to help a frien
Thanks

[uki]

Voltages

V1 pin1 210  pin 2 0  pin6 213  pin7 .03

V2 pin1 209  pin2 0   pin6 208  pin7 .03

V3 pin1 400  pin2 0   pin6 ?    pin7 .06

V4 pin1 150  pin2 0   pin6 150  pin7 .02

V5 pin1 338  pin2 12.9 pin6 337 pin7 12.2

V6 pin1 300  pin2 82  pin6 287 pin7 76

V7 pin3 424 pin6 424 pin8 0

V8 pin3 425 pin6 424 pin8 0

V9 pin3 429 pin6 424 pin8 0

V10 pin3 429 pin6 424 pin8 0


Heater voltages
V1 2.3
V2 2.3
V3 3.0
V4 2.3
V5 3.0
V6 3.0
V7 3.5
V8 3.5
V9 3.1
V10 3.5

[Latole]

I have a fair knowledge of tube amps I mostly do the easy stuff

Heater voltages V1 2.3 V2 2.3 V3 3.0 V4 2.3 V5 3.0 V6 3.0
 V7 3.5 V8 3.5 V9 3.1 V10 3.5

Does not appear to have any mods  this amp has been mistreated imo
I’m trying to help a frien
Thanks

They are low ; too low .

Voltage reading are from the ground ?

You should read 6.3 volts between pins 5/4 and 9 on preamp tubes
From ground  you must have 6.3 / 2 =3.XX not 2.3

[Willabe]

Thank you uki for doing this, much easier to read now!   
 

Voltages

V1 pin1 210  pin 2 0  pin6 213  pin7 .03

V2 pin1 209  pin2 0   pin6 208  pin7 .03

V3 pin1 400  pin2 0   pin6 ?    pin7 .06

V4 pin1 150  pin2 0   pin6 150  pin7 .02

V5 pin1 338  pin2 12.9 pin6 337 pin7 12.2

V6 pin1 300  pin2 82  pin6 287 pin7 76

V7 pin3 424 pin6 424 pin8 0

V8 pin3 425 pin6 424 pin8 0

V9 pin3 429 pin6 424 pin8 0

V10 pin3 429 pin6 424 pin8 0


Heater voltages
V1 2.3
V2 2.3
V3 3.0
V4 2.3
V5 3.0
V6 3.0
V7 3.5
V8 3.5
V9 3.1
V10 3.5

[Latole]

Do you know V7,8,9,10 pin 8 are ground ?
0 volts is right

[Willabe]

Big chief, you need to measure the heaters across their pins, 4/5 - 9, 2 - 7 and not 1 meter probe to a heater pin and the other meter probe to ground. 

[Latole]

Voltages

 

Heater voltages


V1 2.3   = 4.6  heater voltage 
V2 2.3   = 4.6
V3 3.0   = 6
V4 2.3  = 4.6
V5 3.0  =  6
V6 3.0.  = 6
V7 3.5   = 7 !!!!
V8 3.5   = 7  !!!
V9 3.1    = 6.2 Good
V10 3.5 = 7

If you read 7 volts at V8 , you must read 7 volts at V9 not 6.2 
Tubes are wired in parallel

Something wrong with your test meter or amp wiring or.......... ?

[Latole]

Big chief, you need to measure the heaters across their pins, 4/5 - 9, 2 - 7 and not 1 meter probe to a heater pin and the other meter probe to ground.

That is what I wrote 1 hour earlier........

[Big chief]

Pins 4-5 on this amp are tied together
At pilot light from ground on each side 3.1 Across the pilot light 6.2
Pin 8 to ground 0
I have check plate resistors none out of specs  next check coupling caps for dc current I guess

[Latole]

Pins 4-5 on this amp are tied together
At pilot light from ground on each side 3.1 Across the pilot light 6.2
Pin 8 to ground 0
I have check plate resistors none out of specs  next check coupling caps for dc current I guess

Yes 4 and 5 are always wired together, that is what we mean when we wrote 4/5 and pin 9
Read with voltmeter at pin 9 ansd pin 4 or 5 . you should read 6.2 as pilot light

[Latole]

uki wrote ;

If you could provide the schematic it would be a great help.

[Willabe]

....Across the pilot light 6.2

That fine, but because you had lower readings before on the 1st/2nd preamp tubes, best measure that 1st preamp tube again across pins 4/5 and 9. 

[Big chief]

Found some frayed wire going to replace all heater wire then recheck voltages

Thanks for all your time and help

[Big chief]

Repaired heaters wires to all tubes

Have 6.2 on all heaters set power tube bias at -49  all at once all tubes lost power but pilot light stayed on    Now don’t know what to do

[shooter]

all tubes lost power

as in the filaments went out or the B+ went to zero?

[Big chief]

I found the problem loose heater wire  my fault.

However I have dc voltage through the coupling caps should I replace them .1uf

[sluckey]

However I have dc voltage through the coupling caps should I replace them .1uf

Those caps are supposed to have dc on each side.

[Latole]

I found the problem loose heater wire  my fault.

 

Congrat !

Answer #3 february 7

[Big chief]

Have checked ohm’s on all resistors none seam to be more than 10%
Rechecked voltages
V1 pin1 219 pin6 227 V2 pin 1 222 pin6 228 V3 pin1 414 pin6 412 V4 pin 1 230 pin6 232
V5 pin 1 353 pin6 353 V6 pin1 312 pin6 301
V7 pin3 439 pin6 403 V8 pin3 439 pin6 402 V9 pin3 434 pin6 434 V10 pin3 435 pin 6 433

6.2 to all heaters
Power tubes are new and checked  pa tubes test good on my tube tester have replaced some and moved around   Chopped stick board no loose connections   What am I missing  still very low volume

[Latole]

Many tube tester are not reliable, best is to pu know good preamp tubes

[sluckey]

Examine the speaker jacks. Is the plug in the correct jack? Do you have the simple two lug jack for the external speaker? Or is it the more complicated jack with transfer circuit switch contacts as found in later TRs?

You still have not provided a correct schematic for your amp. There are more than one TR circuit with a MV and we cannot guess which one based on the little info you have provided.

[Latole]

You still have not provided a correct schematic for your amp. There are more than one TR circuit with a MV and we cannot guess which one based on the little info you have provided.

Third time we ask 

[Big chief]

I’m using schematic Twin reverb Aa270 layout
I search this web site a d printed the schematic that I’m using

I have not been able to find the exact schematic for this amp yet and I have searched all I know
Have used 2 different speaker cabinets with 4 ohm and have checked and cleaned the 2 jacks that are on the chassis I’ll try my best to take photo of the chassis that I’m working on
This amp is a mid 70’s with master volume

[Latole]

I’m using schematic Twin reverb Aa270 layout
 

Wrong layout ; no master volume

Did you look to my link ? Answer #8
All are there.

Can you read schematic ?
Layout is not good to trouble shouting.

[Big chief]

Yes I can read schematic  I hope I answered your # 8

I am still looking for schematic with master volume now I’m trying to send photo of chassis

Some times I get a little confused

[uki]

Please post more pictures from the other side of the chassis, as well front and back faces, someone might spot the schematic for you with that info !

Oh and about the heater wires, make sure the same wire is in the same pin number for all sockets, unless the schematic says otherwise.

[Latole]

Yes I can read schematic  I hope I answered your # 8

I am still looking for schematic with master volume now I’m trying to send photo of chassis

Show us the right schematic.
Schematic is the first thing you need before working in a amp .

[sluckey]

I am still looking for schematic with master volume now I’m trying to send photo of chassis

Look in Hoffman's schematic library. It's there. Does your amp's MV have a push/pull switch on it? If so, look for that schematic. If not, look for the MV without the push/pull switch.

[pdf64]

The 470ohm unbypassed V3 cathode resistor shown in the photo indicates that this may be the appropriate schematic https://el34world.com/charts/Schematics/files/Fender/Fender_twin_reverb_sf_100_schem.pdf

The previous version without the pull boost has a bypassed 2k2 V3 cathode resistor https://el34world.com/charts/Schematics/files/Fender/Fender_twinreverb_sf_100_mv_noboost.pdf

[Latole]

You have a very good eyes

[pdf64]

I was getting desperate trying to find something to move this along! 

[Latole]

I was getting desperate trying to find something to move this along! 

 

[Big chief]

More Photos

[Big chief]

More Photos

[pdf64]

The resolution of those photos is inadequate for them to be much use. We need to be able to zoom in and get detail, not mush.

[Big chief]

hope these photos are better

[Big chief]

one more time

[Latole]

What is that pot ?

[Big chief]

That pot hum balance for power tubes to the best of my knowledge

Could I possibly have a weak out put or choke problem it seams no matter what I do the volume does not change I have replaced every tube even power tube sockets

[Latole]

That pot hum balance for power tubes to the best of my knowledge

Could I possibly have a weak out put or choke problem it seams no matter what I do the volume does not change I have replaced every tube even power tube sockets

Without the right ( and basic amps repair  ) tools ; scope and audio generator....... good luck