Ampeg V4B RI

[BassAdder27]

I’ve just returned to playing the awesome Smpeg V4B RI ( new version )

I’m looking at re-tubing the power tubes ( match set of 4 )

Anyone got images of where the bias pot is inside the amp ?

I believe it’s R16 ??

Not found any images of the inside of the new V4B or where the bias pot is ?

I have the Ampeg bias instructions but curious to seeing images inside before I start

 

[coreyfyfe]

There is one large trim pot on the pcb near the power tube on the left in the image here. Might be the one you want. As you mention in the ampeg bias instructions it says R16.

Ampeg V-4B + Ampeg SVT-112A + Ampeg SVT-212A

Mein erster Amp war ein (geliehener) Ampeg SVT CL. Für den Einsteiger ein Wahnsinnsteil, leider auch was das Gewicht des Amps betrifft. Ich war heilfroh, dass ich mir kurze Zeit später einen leichteren Amp gekauft habe. Der Sound des Ampegs fehlte mir aber dennoch recht schnell. Leider verfügte...

www.disssa.de

Ampeg provided detailed bias instructions here, I’m sure this is what you’re referencing but for anyone else looking for this information

Post in thread 'New Ampeg V4-B Tube Biasing'

Oct 31, 2013

Our amazing enginner, Dawn, read this and kindly instructed me to clear this up. The image here are the bias instructions for the new V-4B. Maybe there was a mix-up when the schematics were sent, but there is certainly a bias pot. Check with our support guys to get the full schematics. They have a disclaimer you have to agree to before they will send.

• AmpegUSA

https://www.talkbass.com/attachments/v-4b-bia-instructions_zps06996e1a-jpg.2196758/

 

[BassAdder27]

That’s perfect thank you

 

[BassAdder27]

Is it this white pot circled in red ??

 

[maxvockner]

yes that is the trim pot circled

 

[BassAdder27]

Update … New matched set of 4 JJ 6L6GC valves arrived so opened up the V4 ready for a re-valve ( mine is 2019 and had EHX 6L6 valves and it was purchased secondhand so no history )
The amp sounded fine with EHX but I wanted peace of mind with a new set.
Bias check of R12 was running a little hot at 470mvdc ( 450mvdc recommended) checked the other three and all within the Ampeg 400 - 500 guide.
Fitted new set of JJ and set Bias of R12 to 450mvdc
Job done and although you’re not adjusting each valve individually it was done as per Ampeg instructions for the V4B RI model
While it was open I visually looked around and looked clean and as it should. Not sure if a 7year old tube amp would have any other issues due to age but I hope not !!
Note all the R12,R13,R14,R15 resistors have a blob of sealant at each end which you need to get through with your test probes. Mine had already been checked before so I could make contact easily

 

[murphy]

I expect @agedhorse will have a comment also?

 

[Wasnex]

Bias check of R12 was running a little hot at 470mvdc ( 450mvdc recommended) checked the other three and all within the Ampeg 400 - 500 guide.

Sounds like the tubes were running just fine. I don't know Ampeg's tolerance for the amp but +/- 10% is not unusual. At 10% tolerance the acceptable range is to 405mV to 495mV. At 470mV the tube is running within 4.5% of spec.

Definitely save the tubes for backups. Also, you may be able to get them to balance even better by sorting them in a different order.

 

[BassAdder27]

For me although the EHX valves installed when I got the amp second hand sounded fine changing them to a new set of JJ was peace of mind ( gigging amp ) Plus I believe the stock tubes installed the V4B RI are JJ these days ?
The EHX tubes red print on them had discoloured to near brown so I guess the previous owner had them installed for some time. Will be a back up set now

 

[beans-on-toast]

Some general comments..

The Ampeg procedure, step 7, wait 10 minutes in playing mode, can be extended. I like to wait half an hour. Playing through the amp allows it to warm up faster. You want it to reach a thermal steady state where components are no longer drifting. The readings at the tubes should be consistent from one reading to the next.

In North America, the bias procedure assumes 120VAC at the wall. Always note the AC wall voltage when setting the bias. If your wall voltage is higher or lower, the target bias setting will change.

There is hysteresis in the bias pot caused by slack. Initially turn the pot fully CCW as instructed. Then turn slowly up to the desired bias voltage. If you exceed the target, turn the pot CCW again, then turn CW to the desired bias voltage.

Note that the optimal bias voltage is within a range that both sounds good and which allows the amp to remain within a safe operating envelope. Their procedure is basic. A tech can optimize the bias setting using test equipment.