Power transformer diagnosis

Hello all,

I recently purchased a Bugera V55 infinium in a lot of damaged appliances at a local returns outlet. Obviously it is in non working condition. I powered it up and got the Bugera blinking light but no noise. Some searching seemed to suggest a tube issue. I changed a busted tube, and tested the others (all are now in good condition. Amp would turn on, no noise and the blinking light. Tubes were not getting warm in any of the above scenarios.

I began testing the power supply from the outlet in and here is what I discovered.

AC IN from wall (117.8 vac)

Power transformer:
Heater voltages: 1. Across the total winding (no center tap): 3.26vac
2. One lead to ground : 16.57vac
3. second lead to ground: 17.82vac

High voltage: 1. Across the total winding (no center tap): 183.7vac
2. one lead to ground : 71.6vac
3. second lead to ground : 1.48vac

Bias voltage: 1. Across total winding (center tapped) : 20.8vac
2. one lead to center tap: 10.5vac
3. second lead to center tap: 10.5vac

The only one that conforms to how I understand how a power transformer functions is the bias circuit. I'm trying to determine if the transformer itself is blown.

I did also check continuity between the windings:
1. Primary to secondary : No continuity
2. High voltage winding (total winding): Continuity
3. Heater winding : Continuity
4. Bias winding: Continuity

Thanks for your time.

 

The transformer was disconnected from the board when I took the measurements. The tubes did not glow.

 

I think This is the best approach but I don't have another transformer with a bias tap.

 

I pulled the transformer from the circuit before the measurements and just hooked up my voltmeter to the loose leads.

 

If it's a 230-240 wouldn't that also effect the bias circuit? According to the schematic it's designed to put out 20 vac and that part at least appears to be spot on.

 

I will check later on today, but its looking more and more like you guys are correct about the type of transformer. Thanks

 

You guys were right it was european spec. And you caught it quick too. I already replaced the transformer with one I had lying around that fit the bill. I'm going to use another center tapped transformer from a solid state amp for the separate bias voltage. The only other issue is that the new transformers high voltage is center tapped. Can I just use one of the leads and the center tap of the new transformer to sub in for the non center tapped high voltage leads of the first transformer? Thanks again for all your help.

 

I am just going to flip it. My wife would kill me if I tried to use a 55 watt tube head in the house. I got the whole lot (50 appliances) for about $150. I though attempting to fix the amp would be give me some more experience, because I've just started building and repairing my own. And of course I learned something right away (read the schematic, and check the transformer for proper primary voltage). Thank you for your help.