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Post subject: Another DRRI Reverb Problem!
Posted: Sun May 24, 2015 2:47 am
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Since buying my DRRI Fudge Brownie almost 3 months ago I have had problems with the reverb. Initially it would cut out intermittently but that is now ok. Also, the reverb seemed very intense at any setting above 2. A tube change to a NOS Philips 12AT7WC seems to have fixed that.

The latest problem is a hum that becomes noticeable at around 3 on the dial and gets louder as the reverb setting is increased. I am inclined to get a new RCA lead for the reverb but are there any other suggestions as to what could be causing the hum? Even with no instrument plugged in and the channel volumes off it is still there. The only way to stop it is to tun the reverb off!


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Post subject: Re: Another DRRI Reverb Problem!
Posted: Sun May 24, 2015 2:56 am
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Sounds like microphonic tube. Try replacing the 12AX7 recovery tube (V4) with a known, good 12AX7.

It might be that new Philips 12AT7WC. Though I have yet to have issues with this tube. Or any Sylvania/Philips 12AT7W(A to C).

Good luck!


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Post subject: Re: Another DRRI Reverb Problem!
Posted: Sun May 24, 2015 4:55 am
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Thanks for the suggestion.

When I removed the tube I noticed that some of the pins were bent and perhaps they were not making a good contact so I straightened them. I put the tube in V1 and tried the pencil/rubber tap test and it seemed ok so I put it back in V4 and it now seems much better. Certainly not as noisy as it was.

I also noticed that all of the pins were coming out of the base of the tube at an angle so that if you stand the tube on the pins it is not upright. This could mean that the tube is touching the inside of the tube sleeve. Could this create noise?

There is still some hum but that has always been the case since I got the amp. It is usual for the DRRI to have some hum in the reverb that increases when the setting is increased?


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Post subject: Re: Another DRRI Reverb Problem!
Posted: Sun May 24, 2015 11:41 am
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fifty4 wrote:

There is still some hum but that has always been the case since I got the amp. It is usual for the DRRI to have some hum in the reverb that increases when the setting is increased?



No , check Reverb wires and RCA jack if you have good ground . At the amp and at the reverb pan .

Noisy tube ?


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