Vox AC 30 Standby LIght Blinks with Tremolo

[Perkinsman]

Upon powering up cold, the standby light comes on but is a little noisy, then after 30 seconds warmup, the noise disappears for good.. then when I turn the tremolo on, the standby blinks in time with the trem...is this normal for this amp and if not, what's the most likely problem?

[g1]

There are so many different AC30 versions that have been built. Please post the exact schematic for this particular unit.

[Perkinsman]

Sorry about that, it's the CC2x. I've seen several posts regarding problems with the standby blowing rectifier tubes. Vox resolved this by adding a 5W resistor to the standby switch. If this unit doesnt have one, I can add it but how many ohms should I use & would it just be soldered across the leads of the standby switch?

[Pedro Vecino]

I think it is not necessary. Simply turn the amplifier on and off with the power switch only.
As for the flickering of the pilot lamp when activating the tremolo, I have seen it sometimes. It´s very likely to be accompanied by a hum noise on every oscilation. In my case it came from a serious imbalance in the power tubes.

[Perkinsman]

I may change the power tubes. Do they have to be a matched set in this model?

[g1]

Poor matching was what Pedro meant when he said imbalanced tubes in this model can cause the issue you are having. So a matched pair may cure the issue. It's worth a try, if it doesn't help you can keep them for something else.

[Pedro Vecino]

It would be appropriate if it were possible to previously measure the current flowing through each tube. I always do it. Normally I use tube socket adapted to measure the plate current with an ammeter. It can also be measured through the cathode.
If you find very different values you can distribute them as symmetrically as possible between both sides (1/2 and 3/4) trying to make both sides form a similar sum. For example, if you find values of 45, 48, 30, and 36 mA, you can distribute them as 45 and 36 mA on one side (1/2) and 48/30 on the other (3/4). This often helps reduce flicker and associated hum while achieving a rounder sound.
These tests are also used to determine if any tube is inactive, which could create a similar effect due to the imbalance it would create.
If you cannot do these previous measurements and you are going to buy a quartet, it is better that it is matched.
Excuse my poor English.

[Mick Bailey]

Sorry about that, it's the CC2x. I've seen several posts regarding problems with the standby blowing rectifier tubes. Vox resolved this by adding a 5W resistor to the standby switch. If this unit doesnt have one, I can add it but how many ohms should I use & would it just be soldered across the leads of the standby switch?

If you want to do this a 47k/5w resistor is fine and will charge the caps enough to prevent the rectifier from getting stressed. Solder it right across the switch. The side-effect is that in standby you get some low-volume audio - it doesn't mute the amp completely. The value isn't too critical - 47k to 100K is the useful range. I stick to 47K as it charges the caps to fair voltage (80v or so) quickly enough between switching the amp on and using it. I agree with Pedro regarding ignoring the standby switch and advise owners to leave the amp with the standby switch in 'operate' mode.

[drewl]

Since a 5AR4 has to warm up before rectifying, I pulled the Standby on my AC30 TBX and added a post phase master volume in it's place.

[Pedro Vecino]

There is one more element that contributes to that problem that I forgot: the filter selection between 22uF and 44uF. This is important as 22uF is very limited filtering.