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Post subject: DRRI changes tone / volume as gig progresses?
Posted: Mon Mar 26, 2012 9:55 pm
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Just wondering if anyone else has experienced this.

I have a DRRI that seems to get "thinner" and quieter as the gig progresses. It's not the end of the world, just annoying - I like the tone at the start and usually just put up with it by the end of a 3 set night.

Since I noticed the issue (happens even during a 1 set gig) I've been modding the amp and have swapped out all the transformers (power, output, reverb) for Mercury magnetics iron, upgraded the speaker with a Weber 12A125A and replaced all the tubes at least twice (it's been a few years). I've also removed the bright cap. I didn't do these things to solve this particular problem - was just partly tinkering and partly looking for a warmer but cleaner sound - I play western swing style music with an archtop that has a P-90 in it.

I thought maybe it was just ear fatigue or something but I loaned the amp to a friend recently and he asked me if I knew that it got quieter over the course of a set.

Any ideas?


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Post subject: Re: DRRI changes tone / volume as gig progresses?
Posted: Mon Mar 26, 2012 10:15 pm
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Sounds like a gradual decrease of the B+ supply.

Checked your GZ34 lately?

Arjay

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Post subject: Re: DRRI changes tone / volume as gig progresses?
Posted: Tue Mar 27, 2012 10:09 am
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Thanks Arjay! I haven't checked the rectifier.

To be honest I don't know how - oops!

I suppose I could open it up and measure the B+ voltage then let it run for a couple hours and check it again.

Or just get another tube?

thanks again for your help,
dave


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Post subject: Re: DRRI changes tone / volume as gig progresses?
Posted: Tue Mar 27, 2012 10:29 am
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I suggest getting another known good 5AR4/GZ34 to compare to the one in your amp. Another thing that can cause the volume to drop with time, is if the output tubes are biased a little on the "hot" side. My experience with Mercury Magnetic trannies is they put more B+ onto the plates, compared to OEM trannies. And they have greater current output, throughout the volume range.

If the tube start overheating, they made have a tendency to lose efficiency. May want to have the idle bias checked & check to be sure you have adequate air space behind the amp to let hot air escape.


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Post subject: Re: DRRI changes tone / volume as gig progresses?
Posted: Tue Mar 27, 2012 10:52 am
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OK - the plan is to get another rectifier and see what happens. I'll update the thread once I've done that. Thanks!


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Post subject: Re: DRRI changes tone / volume as gig progresses?
Posted: Tue Mar 27, 2012 10:56 am
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If you have a multi-meter you could get one of these and check the plate voltage of the tubes after leaving the amp on for a few hours.

http://www.amp-head.com/product_info.ph ... c9587ff6ba

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Post subject: Re: DRRI changes tone / volume as gig progresses?
Posted: Tue Mar 27, 2012 1:25 pm
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If our suggested remedies do not cure the problem, try touching up all of the solder joints on the power-tube sockets -- if one or more of those is marginal, it could also cause the symptoms you've observed.

HTH

Arjay

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Post subject: Re: DRRI changes tone / volume as gig progresses?
Posted: Sat Mar 31, 2012 12:02 pm
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Thanks again for all the tips - just waiting for a new rectifier to show up then I'll post my results.


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Post subject: Re: DRRI changes tone / volume as gig progresses?
Posted: Sat Mar 31, 2012 3:40 pm
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Keep us up to date.

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Post subject: Re: DRRI changes tone / volume as gig progresses?
Posted: Wed Apr 04, 2012 7:44 pm
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So the parts arrived and I made some changes. I have to confess that I shotgunned a couple things since not much is available locally and I am too cheap to pay to ship things piecemeal.

But first - a confession - I totally forgot that years ago when I was playing more alt.country type stuff I changed the rectifier to a 5R4GA because I wanted the amp to be quieter and to break up earlier. I was a bit embarrassed when I looked at the tube. Ooops.

I ordered a Sovtek 5AR4 rectifier, some new light bulbs, and a Phillips 12AT7WC for the phase inverter position. I've got nothing against NOS tubes, and had some Marconi 12AT7s before but am feeling cheap so that's what I did.

I installed that stuff then rebiased the amp with my multimeter and my Weber Bias Rite BR-AH. With the old rectifier I had set it at 19 because it sounded cleanest there. With the new rectifier it was reading 30 so I dialed it back down to 19.

I had a 90 minute rehearsal today and I'm happy to report that the amp sounded cleaner and the tone was much more consistent over the course of the 90 minutes. The light stayed the same brightness all the way through.

I won't really know until I gig with it this weekend but things are looking positive.

I'll post a follow up in case someone else stumbles across this with a similar problem sometime.

Thanks again to everyone who offered advice, especially Arjay who first pointed me in the direction of the rectifier and explained a bit about the B+ voltage.

I like it here - hope it's ok if I stick around.

dave


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Post subject: Re: DRRI changes tone / volume as gig progresses?
Posted: Wed Apr 04, 2012 8:47 pm
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Glad to hear it all worked out, Dave.

Let there be rawk!

8)

Arjay

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Post subject: Re: DRRI changes tone / volume as gig progresses?
Posted: Sun Apr 08, 2012 10:53 am
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last follow up on this - 3 set show last night - the amp's tone stayed much more consistent than before - didn't "thin" out - and the light stayed same brightness all night

thanks again


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Post subject: Re: DRRI changes tone / volume as gig progresses?
Posted: Sun Apr 08, 2012 1:03 pm
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Congrats!

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Post subject: Re: DRRI changes tone / volume as gig progresses?
Posted: Sun Apr 08, 2012 4:40 pm
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RAWK ON!

8)

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: DRRI changes tone / volume as gig progresses?
Posted: Tue May 01, 2012 8:40 pm
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I have no idea what most of these cats speak of but my tone gets better through each set.. maybe it is the beer? :)


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