Framus Ruby Riot 2 blowing mains fuse

[Emetal]

Framus Ruby Riot 2 blowing mains fuse when only power switch is ON, STBY is OFF. So only heater circuits and pilot light cause the fuse to blow? Tried with current limiting bulb, I can even play. But without current limiter fuse blows. Tried every tube in every place, no single tube in any place will blow the fuse. It can hold all the pre-amp and two of the power tubes without blowing, over that it blows the fuse. Talking about ONLY power switch ON. Bridge rectifier is OK, IC2 and IC3 OK, the only weird measurements are: main transformer secondary output instead of 5 VAC has 9,8 and also the output that should have 2x200 VAC has 2x300 VAC. So the rectifier tube is getting 600 VAC instead of 400 VAC. I do not have much experience, is this a problem? Any other ideas please...

[The Dude]

Is the transformer primary wired/configured correctly (series- not parallel)? With your measurements, it almost seems like you could be supplying 230VAC to a 115VAC input.

Edit: See last page of schematic for transformer wiring.

[Helmholtz]

What's the amp's history?
Did it work fine before at your mains voltage?
Do not try to operate the amp without the bulb limiter. The high secondary voltages could cause a lot of damage.

[Emetal]

Is the transformer primary wired/configured correctly (series- not parallel)? With your measurements, it almost seems like you could be supplying 230VAC to a 115VAC input.

Edit: See last page of schematic for transformer wiring.

I am in Europe but it is wired correctly, yes I checked last page.

[Emetal]

What's the amp's history?
Did it work fine before at your mains voltage?
Do not try to operate the amp without the bulb limiter. The high secondary voltages could cause a lot of damage.

Friend bought this amp on sale as a B stock from Thomann store less then year ago. Had problems and issues from very beginning, last time was brought to me 6 moths ago with with hissing and popping, I replaced power tubes (that were basically new) and it was ok for 6 months, and now problems again. I am starting to think this amp has faulty mains transformer straight from factory.. But it did work for at least those 6 moths, weird.. Without bulb limiter it simple blows the fuse as soon as I turn the Power switch on.

[The Dude]

What is the DCR of both primary windings? They should be similar.

[Mick Bailey]

Does Thomann still offer their 3 year warranty? They've been excellent at arranging collection and repair/replacement of faulty goods at no cost to the customer, even from over here in the UK. Check if the amp is still under warranty as it could save spending on it.

[Emetal]

What is the DCR of both primary windings? They should be similar.

Yes, both are around 9 Ohms

[Emetal]

Does Thomann still offer their 3 year warranty? They've been excellent at arranging collection and repair/replacement of faulty goods at no cost to the customer, even from over here in the UK. Check if the amp is still under warranty as it could save spending on it.

Yes they do in normal countries. This is Serbia, where equipment is smuggled in to the country by people with connections, in order to avoid crazy Serbian Customs. So once you get it in, it's hardly feasible to return anything.

[Emetal]

OK I checked transformer outputs again, with new multimeter: 6,3v, 5v and 17v are OK. The only one that is higher is the one that gives out 2x300 v. On page six of the manual it says it should be 2x200 and on the page nine it says 2x250. So maybe 2x300 is not so bad. Any other ideas what could cause fuse to blow?

[Helmholtz]

OK I checked transformer outputs again, with new multimeter: 6,3v, 5v and 17v are OK. The only one that is higher is the one that gives out 2x300 v.

So it looks like the HT voltage was 2x300VAC from the beginning.
I think this is too high.
It will result in a plate-to-cathode voltage of around 360V for the EL84s. Plate and screen limits are 300V.
Combined with the low value cathode resistor it will result in severe overdissipation, certainly over 120%.
So I would expect the amp to eat tubes.

The least thing you should do is to raise the cathode resistor to 68R/10W.
Make sure the EL84s are still good.

[Emetal]

So it looks like the HT voltage was 2x300VAC from the beginning.
I think this is too high.
It will result in a plate-to-cathode voltage of around 360V for the EL84s. Plate and screen limits are 300V.
Combined with the low value cathode resistor it will result in severe overdissipation, certainly over 120%.
So I would expect the amp to eat tubes.

The least thing you should do is to raise the cathode resistor to 68R/10W.
Make sure the EL84s are still good.

Yes I can definitely replace R82 from 47R/5W to 68R/10W. I do have few questions:

-If the high HT voltage was problem, wouldn't that manifest AFTER switching Stand By On? The fuse on this Amp pops right after Power switch On.

-Would high HT have big negative impact on pre-amp tubes since they are more resilient. I did measure plate voltages of V1A=409v, V1B=395v, V2A and V2B were 409v

-How would I know if any EL84 is bad, I only have multimeter and there is no shorts, only proper ohms between heaters

[Helmholtz]

-If the high HT voltage was problem, wouldn't that manifest AFTER switching Stand By On? The fuse on this Amp pops right after Power switch On.

Ah yes, I overlooked this important info.
Could be a problem with the rectifier tube.
Pull the GZ34 and try again.

BTW, I just saw that the first filter cap is 220µ/350V. Way too large capacitance for a GZ34, especially with hot-(standby-)switching as used here.
GZ34 limit is 60µF. Also a 350V cap rating is too low. What a poor design!
https://frank.pocnet.net/sheets/128/g/GZ34.pdf

[DrGonz78]

So you are measuring 409vdc B+ voltage running through a 350v capacitor? Is there a different rated cap in the amp compared to the schematic?

[Helmholtz]

I did measure plate voltages of V1A=409v, V1B=395v, V2A and V2B were 409v

I guess that is with power tubes pulled?