Marcc Thanks for the response, but I still don't quite follow whats going on to give the numbers on the datasheet, though I do understand the concept of equivalent DC power.

Are you saying that the output of the power transformer is specified as RMS voltage and the output of the rectifier is specified as DC? Or are you saying that are voltages are all specified as RMS?

Either way though this doesn't work out mathematically, do you have a copy of the HMV 01 chassis TDS handy, perhaps you could highlight what is going on in this specific circumstance?

For instance if the voltage at the transformer is 222VRMS then that yields Vpp=222*1.414=313.90Vpp with a forward voltage drop across the original selenium rectifier of 5-10V that yields DC is the range of 300V or an RMS of 212Vrms, neither of which match the specified 245V on the TDS.

Or is the forward voltage drop across a selenium rectifier that I used incorrect (I got this rough number off the web)?

Thanks for the help so far.

Removed Duplicate post

All the HMV O1 Electrogram related stuff is to be made available here for the benefit of anyone following this thread.

A JR copy is also included as it has a modified circuit which is not included in the manufacturers material.

HMV O1 88 Data Sheet
HMV O1 Model Data Sheet
HMV O1 Service Manual
HMV O1 Technical Specification
HMV O1 Technical Data Sheet 66
HMV O1 Technical Data Sheet 71

I have realised our old HMV record player here has a type 01 Chassis (needs a new cartridge: BSR)

I have its circuit and I replaced the toxic waste rectifier. What it shows is that the silicon rectifier is producing 300VDC I added an E cap at the rectifier and two 1.5K 5 Watt resistors in parallel to drop B+ to 245 on load.

At 300V on load I would use 500 preferably 600V filter caps.


Marc

Hi Israel, I encountered on of those 24+24 μF caps on my HMV Nippergram, they are basically 2 24μF capacitors in one and can and should be replaced by 2 normal modern 450-500 volt 22μF electrolytics. These old caps go bad, as I recently found and short out, or just stop doing what they are supposed to and other components suffer consequentially, resistors, transformers etc. The fact that the primary of one transformer has gone open circuit indicates to me that one or more caps have gone bad and I would stress that replacing all of the paper and electrolytic caps is most important!
Cheers.

Be careful when soldering. From memory those had the first of the clear plastic jacketed "Styroseal" caps. The physically smaller ones often did not appreciate a lot of heat from soldering & the use of a Hemostat or other form of heat sink is advised.

Marc

Yeah I plan to go through and replace most of the guts as even the point to point wires look tired. This should be a lot easier given the circuit diagrams provided. Also thanks to JamieLee on confirming the nature of those caps. I'll also be replacing the diodes etc.

Why would you want to replace all these probably perfectly good parts?

I would check the resistors, but I see no worthwhile purpose in replacing the styroseal caps nor any polyester ones.

Partly for fun and partly to learn about the circuit. But primarily because it is going to a friend and I want it to be rock solid lest it break down or worse. It will also ensure that the circuit biasing is correct, as older resistors can drift in value quite a lot, not to mention that many of the older poly caps are +-20% compared to most modern ones that are +-10%.

Also I notice that Marcc used 2x 1.5k 5W in parallel are his series resistance with the newer silicon diodes, is this safe? as the data sheet mentions that these resistors should act as a fuse in case of AC sort to ground. At twice the rated wattage (10W as two by 5W resistors) would this not defeat the purpose? Or have you inserted a separate fuse on the AC line?

I used those resistors as they gave me the correct OP voltage. This one has never given trouble from shorts, it has never had a fuse. The idea of putting the resistor where they did in the AC, is not new. They often did that with 6X5 as it was a valve that had designs up until it was made more like a 6X4 & the Russian Sovtec 5Y3, of going short. Pretty disappointing for a valve designed for car radio. The other reason it is there is to cut the surge current when the caps charge.

By having a resistor in the B+ that "sails with the wind" any massive overload will see it burn, acting as "fusistor" That is why I also never recommend beefing up a back bias resistor: Better it burn than the transformer.

I recently restored the valve amplifier in my 1960 Rock-Ola jukebox which had a selenium bridge rectifier to supply the B+ voltage. After I replaced the filter caps I tested the output of the selenium rectifier. Under load the output of the selenium rectifier had dropped to 200 volts. The circuit diagram specifies the DC voltage should be 250 volts. Apparently the voltage drop across a selenium rectifier increases with age. I replaced the selenium bridge rectifier with a 1000v 10amp silicon bridge rectifier that cost $5 from Radio Parts in Melbourne and installed a 68 ohm wire wound resistor to drop the B+ voltage back down to 250volts as specified in the circuit diagram as well as to limit the current when the filter caps charge as the amp is switched on. There is also a 1 amp fuse installed between the secondary winding of the power transformer and the new silicon bridge rectifier to protect the transformer in case one of the silicon diodes shorts in the new rectifier.
The amp is working well and sounds great.