Restoring my Telefunken Opus 7 - some pointers welcome

[majoco]

EL84's do run pretty warm, but it's strange that the pair are different temperatures especially as the one out in the clearer air is the one getting hot. Is it a push-pull output stage or bi-amped with one amp for each bass speaker. Check the value of the cathode resistor, the cooler running one may have gone high which will cause your distortion maybe....and yes, EL84's can and do suffer from grid emission when they get old - measure the voltage across the cathode resistors - they should be about equal and a reasonable value, say 6 volts or so IMHO.

[radix39]

Originally Posted by majoco

EL84's do run pretty warm, but it's strange that the pair are different temperatures especially as the one out in the clearer air is the one getting hot. Is it a push-pull output stage or bi-amped with one amp for each bass speaker. Check the value of the cathode resistor, the cooler running one may have gone high which will cause your distortion maybe....and yes, EL84's can and do suffer from grid emission when they get old - measure the voltage across the cathode resistors - they should be about equal and a reasonable value, say 6 volts or so IMHO.

Its push pull as far as I know, especially since its mono only output.
Right now everything is out of the chassis, so there is plenty of airflow. I can feel the heat rising from the top of the EL84's, but one of them is certainly hotter. I cannot touch it with my fingers - its about as hot as a 40w light bulb i'd estimate. I'll check the resistors tomorrow.

As an update, I replaced about 10 more caps this evening. At this point pretty much all of the high voltage paper caps that were leaking/melted are replaced. I tested after each replacement, unfortunately I didn't hear too big a difference after replacing one.

The last one I did for the night was disconnecting the 50/50uf can at the top, and putting new ones on the underside. After turning it back on (and hoping they wouldn't explode ) I was greeted to a HUGE improvement in sound. Almost all the distortion is gone at this point, and the volume and clarity are much improved. The amount of bass this guy puts out is amazing! There is still a little bit of "looseness" to the sound, especially in the lower frequencies, but I hope that the remaining caps will fix that.

There is still one electrolytic left to replace - a 2uf unit. I ordered one online since I couldn't find it locally, however what came was a 2uf unit, but not an electrolytic. The voltages exceed the original, but i'm not sure if I can replace an electrolytic with a non-electrolytic. Would this be ok?

[jeffsod]

Nice to see you are making some progress with this incredible radio. I wish I could answer your question on substitution but can't. Maybe someone on the Tube audio subforum could?

[analog]

When you say hot do you mean the plate is glowing red? If so the coupling caps NEED to be replaced. Do not operate it like this for any length of time as the tubes are quickly going to be ruined,. EL84s do run hot normally, and probably much hotter than the RF tubes in the set but should never run with red plates.

[amptramp]

I had a Heathkit amplifier with push-pull EL84 outputs where one output tube ran hot after a few minutes of operation. The cathode bias voltage was going down. Removing the electrolytic across the cathode bias resistor eliminated the problem.

[radix39]

Originally Posted by analog

When you say hot do you mean the plate is glowing red? If so the coupling caps NEED to be replaced. Do not operate it like this for any length of time as the tubes are quickly going to be ruined,. EL84s do run hot normally, and probably much hotter than the RF tubes in the set but should never run with red plates.

When I say hot, I don't mean the plates are glowing. I just mean the tube is physically very hot. Most of the tubes I can actually touch and hold for a few seconds without burning myself. But one of the EL84's is more like a 60w lightbulb after its been on for a while - you can't touch it without burning your fingers. Everything seems to be running well so I assume its ok. I'm sure there are some resistors that are out of spec but replacing them would be such a chore.

[Telecolor 3007]

I'm gelaous on you, U.S.A. guys. The tube radios made in West Germany for U.S.A. market had all F.M. band (88-108 M.Hz.), whyle the one ones made for Europe had F.M. only on 88-100 M.Hz., and some, later on 88-104 M.Hz; and in Bucharest 2 of the stations that sometimes I listen much are on 106.7 and 107.3. I had an "Grunding" radio made for U.S.A. market ... but it wasn't sounding to good (bad caps I think), and it broke, and stupid me just salled it... now I regret that I did that, becuase it'll be very hard to find an full range F.M. radio with electronic tubes (valves)... probably I'll by one from U.S.A. when I'll have the money (one that will be stereo with 4 speakers - the front speakers to have the same size, and the 2 side one to have the same size between them to and to have the stereo decoder installed).

[wa2ise]

Originally Posted by radix39

There is still one electrolytic left to replace - a 2uf unit. I ordered one online since I couldn't find it locally, however what came was a 2uf unit, but not an electrolytic. The voltages exceed the original, but i'm not sure if I can replace an electrolytic with a non-electrolytic. Would this be ok?

That will work fine, maybe better than an actual electrolytic. It won't dry out like a lytic can can.