Diplomat sudden problem

I was listening to my Diplomat at lunch time to enjoy some FM radio. after about 10 minutes I hear a little click or pop,, then a loud hum audio hum on one channel and can't get rid of it with the tuner pre-amp,,I still hear music from that channel dimly but still hear it. I took out the top fuse,, hum went away as well as the bass,, It won't leave if I take the RCA out of the input or anything. I ruled out the pre-amp (thank God) ruled out the three tubes on the power amp,, The only thing it can be is a transistor or a capacitor. Or could it be something else? Has anyone else had this happen to them??? What could it be?

More than likely one of the caps in the Amp let loose. Recapping the whole amp should take care of the hum. The lytic's in the 49A and 59A tend to be pretty well dried out. I did one for a friend a while ago and everyone was leaky and the can's were completely DRY! Mine did the same thing 2 days ago. One side, BIG HUM and the sound went tinny. Gonna have to tear it down and see what's what.



Larry

larryderouin said:

More than likely one of the caps in the Amp let loose. Recapping the whole amp should take care of the hum. The lytic's in the 49A and 59A tend to be pretty well dried out. I did one for a friend a while ago and everyone was leaky and the can's were completely DRY! Mine did the same thing 2 days ago. One side, BIG HUM and the sound went tinny. Gonna have to tear it down and see what's what.



Larry

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Yes exactly!!! real loud hum ands tinny sound. So it is a cap? Ok I will take it out tonight and order caps.. Are you talking about the big power caps or ones under the chassis? I know the values of the main caps.. gotta call mouser and order them.. I am thankful it isn't the tuner preamp

Replace all of them inside and the 3 can caps. The 3000uf caps are a voltage doubler so watch your connections. Should run about $40.00 (Incl shipping) for them all.

Larry

larryderouin said:

Replace all of them inside and the 3 can caps. The 3000uf caps are a voltage doubler so watch your connections. Should run about $40.00 (Incl shipping) for them all.

Larry

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is Mouser where you would go for these? Or is there a better place? Will this hav better bass once I recapp the amP? Someone told me the first to go with bad caps soundwise is the bass. Thanks again Mike.

Bass isn't gonna change much if any, as the finals are transistors and the 6HU8's don't have a lot of gain. With the way it's designed, I think the interstage transformer in the middle soaks a good bit up. The 49A/59A isn't inherently bass heavy. I personally think it's voiced more for classical, than rock or even jazz(older crowd...WWII Generation). But it will probably tighten up a bit.

Mouser is where I get my caps. nichicon UPW series (all radial caps and I add lead to them so they fit where an axial would go.) If you insist on Axials use the tvx series. otherwise UPW's or UKL's if UPW's aren't available. I use Cornell Dublier DME series film caps (they are small and fit well) instead of Orange drops.

Larry

Is it ok to listen to, when I pull the two speaker fuses? the stereo is the only thing I can listen too till I move all my stereos to my new location. What do those two fuses do? anyway.

NO! The fuses are the "protection circuit" for the speakers and the amp. Those germanium transistors are very fragile electrically. Why take chances you don't need to.

Before and After pictures of the 49A I did a while ago. There are 3-390oHm 3watt resistors (cement filled ceramics) in the upper left corner under the 2 can caps (see terminal strips). Those should be changed out. After 45+ years of heat related abuse, it's cheap insurance. Use 390oHm 5W . The two caps on the terminal strip at the bottom and the two to the right are the replacements for the 4 section "silver" can cap. the Cardboard ones got restuffed. There are 4 gray ceramic resistors attached ot each transistor. Don't touch them unless they are bad. There is also a thermal diode (looks like a transistor with 2 leads. This is the upgraded bias circuit. This is not available at ANY COST! Leave it alone. However if any are blown you can revert to the original version of the bias setup.





Make sure you have the latest version of the 49A-49T manual. It's the one with the tuner face on the cover. And it will have BIAS Modification instructions in the amplifier section of the parts list.

Larry

My Goodness there is like ten times as much under that chassis then my magnavox series 100 amp!!!! Much much more. I will take your advice. Thanks so much Mike.

If this amp is gone,,, is there a way to make the tuner/pre-amp stand alone? has anyone done that before? Thanks again

That's nice work Larry.

Thanks Larry I found the right manual.. I am going to work on the recap soon. I freed the tuner on the other chassis. I am going reinstall it in that Royal Electra console and listen to that for a while. Then work on the diplomat. I wonder if the Royal Electra has more bass? Anyways Thanks for your help. Wish I could send it to you instead. I am not a professional and I rather not try this at home,,,,, Ohwell nothing ventured nothing gained.