Kenwood KW-70 Receiver

[ALBQ]

Parting Shot

All,
Parting shot of receiver playing and tubes healthy glow. I let the receiver play in my office for an hour or two to make sure everything was all right before closing it up. I then moved it to my listening room and hooked it up to my back-up speakers, where it played happily the rest of the day.
Thanks to everyone for their help -ALBQ

 

[slor]

Posted Elsewhere, But....

...This thread is really much more relevant to my problem:

I'm trying to get a Bell 2440 integrated amp (4 x 7189A, plate voltage is 420) up and running. I put in a quad of Sovtek EL84Ms, but after the variac gets much above 100VAC the tubes start running away.

I've heard conflicting advice as to whether an amp calling for 7189A needs the tube sockets rewired to accept EL84M...anyone have a definitive answer?

Also, a tech recommended installing a bias trim pot (the bias is fixed but non-adjustable). The schemo wants -19 (and the tubes are currently getting -18) and I'm hoping that bringing that down (I should say, making the bias voltage more positive) will get the tubes under control (I may also add a dropping resistor to the power supply to try and shave off a few volts there. If anyone has any further suggestions, I'm all ears! And yes, I have replaced the coupling caps!

Thanks,
Seth

 

[DigitalJunkie]

Making the bias more positive will only make the tubes draw more current.

Not sure about the sockets,do the 7189 and EL84 share the same pinout?

Hmm,are there any connections to pins 1 and/or 6 on the output tube sockets? That appears to be the only real difference between the two -the 7189 has pins 1/6 connected to the grids.

420V B+ is about 120V too much for EL84's,according to the datasheets. You can probably run them a bit over the plate voltage ratings,if you drop the current through them a bit. (trying to keep the total *power* within spec's.)


Hope you're enjoying the weather lately..Gonna be a warm weekend!

 

[slor]

Thanks for the reply, and yes: It's already quite warm enough, thanks!

Speaking of warm, the tubes I'm using are EL84M, which I'm told is rated for a higher plate voltage than EL84. I'm also told that this type is more amenable to higher current than higher voltage, so it seems as though it's worth a shot....

Thanks for the pinout tip, I'll check the schemo and refresh my memory....

 

[nuvistordave]

I usually lurk on Fleabay for a cheep Stereo 40; the OPTs on these are excellent and are 8K pri; 4-8-16 sec. These will swap right in to just about any 6v6/EL84 type amp and upgrade the thing right into high fidelity.