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OLDER DECWARE GEAR SUPPORT >> SE84A, SE84B, SE84C, SE84C+,SE84CKC >> SE84A?
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Message started by quietglow on 12/05/12 at 00:52:19

Title: SE84A?
Post by quietglow on 12/05/12 at 00:52:19

I have an SE84A with a hum problem. Is this where I ought to ask it?

Thanks!

Title: Re: SE84A?
Post by Rivieraranch on 12/05/12 at 00:59:17

You have come to the right place.

Have you had it all these years or bought it second hand? What is it connected to and when does it exhibit the hum?

Title: Re: SE84A?
Post by quietglow on 12/05/12 at 01:07:29

Awesome. My amp is second hand -- I bought it from the original owner.

I am a relatively experienced amp owner (i.e. I've built a few tube amps from scratch, though its been a few years). I adore my SE84A, but it's developed an intermittent hum. The hum comes from both speakers and comes and goes. It's definitely something out of the ordinary (it's louder than the base hum). Interestingly, flipping the bias switch a couple of times seems to usually makes it stop temporarily. I haven't been able to determine if its still there if I pull the input tube.

Any ideas of what to check? I have a multimeter and can test.

Title: Re: SE84A?
Post by Lon on 12/05/12 at 02:11:29

Hi quietglow, and welcome to the forum.

I think this may be related to the switch or the connections the switch has. UNLESS it's the input tube. I would try other input tubes, and I would take a look at the switch an its connections.

Title: Re: SE84A?
Post by quietglow on 12/08/12 at 05:02:26

Okay so I did some more testing: when the hum is going on, I turned off the amp and removed the input tube. The hum was unchanged. Then I removed both output tubes. No hum. Then I replaced the output tubes one at a time. With either tube, in either channel, there was hum on that channel (i.e. when they were both in, there was hum on both channels).

This means its not input tube or switch right? I suppose its possible that both output tubes are bad, but that seems rather unlikely?

Title: Re: SE84A?
Post by quietglow on 12/08/12 at 05:11:28

How do people handle having the volume pot on the amp? I use a preamp for volume control and I've just left my SE84A with the volume pot at max. Maybe the output tubes are cooked after all.

Title: Re: SE84A?
Post by Rivieraranch on 12/08/12 at 13:25:55

You can ride the gain, i.e. adjust both devices to see what sounds best. It could be recording dependent at times.

A fresh tube set would bring the unit to life again. You have solved the hum problem.

Title: Re: SE84A?
Post by opnly_bafld on 12/08/12 at 14:50:47

"How do people handle having the volume pot on the amp? I use a preamp for volume control and I've just left my SE84A with the volume pot at max."

When I used mine with a preamp I set the vc to just short of max, worked great this way.