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Post subject: Rectifier Tube Swapping?
Posted: Fri Feb 22, 2013 6:50 pm
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Ok guys...will this work and will it harm your amp?

-Swapping out your 5AR4/GZ34 with a 5R4 is a great way to lower the volume/sweet spot of more powerful amps like tweed Bassmans and Super Reverbs. 5R4's have the same pin-out and heater current as a 5AR4/GZ34, but decrease your amp's plate voltage by 30-35 volts.

Looking for some input.

T2

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Post subject: Re: Rectifier Tube Swapping?
Posted: Fri Feb 22, 2013 7:08 pm
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That's Beemers territory.
But I'm pretty sure I saw him say it works ???
I'm sure he will catch this

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Post subject: Re: Rectifier Tube Swapping?
Posted: Fri Feb 22, 2013 8:12 pm
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Yeah, until Beemer arrives, the 5R4 would certainly do the job without increasing the heater current. I think the 5R4 GBY is the way to go. Lost my tube spec references on this computer. But the 5R4 has a directly heated cathode, akin to the 5Y3 and 5U4GB. Without the tube specs, I'm not sure of the ma capacity. Can any one steer me to a tube spec site? Tried Seymour Duncan, but no luck. Thanks, Art

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Post subject: Re: Rectifier Tube Swapping?
Posted: Fri Feb 22, 2013 9:17 pm
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Blues and Art...thank, seems I remember Beemer saying this would work, but danged if I could find the post (or it might have been an e-mail). :oops: I kind of hoped he would be by tonight, but I guess I am not in that big of hurry.

T2

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Post subject: Re: Rectifier Tube Swapping?
Posted: Fri Feb 22, 2013 9:23 pm
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He must be on 3 to 11's

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Post subject: Re: Rectifier Tube Swapping?
Posted: Fri Feb 22, 2013 10:05 pm
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From the KCA NOS Tubes website:

https://www.kcanostubes.com/content/rec ... lity-chart

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Post subject: Re: Rectifier Tube Swapping?
Posted: Fri Feb 22, 2013 11:53 pm
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Thanks, Bill !!! Checked a few of my old haunts, but didn't spend enough time to get the full spec on the 5R4. Do you have the the max ma output for this tube? Didn't see any access to the specific info on the site, you provided. But I probably missed something! Art

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Last edited by aclempoppi on Sat Feb 23, 2013 12:20 am, edited 1 time in total.

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Post subject: Re: Rectifier Tube Swapping?
Posted: Sat Feb 23, 2013 12:10 am
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I don't see a problem as long as a few amp-safety protocols are observed -- namely ensuring that the power-supply's filter caps are up to the task (in the case of swapping to a higher-output rectifier) and re-biasing the tubes in the final drive stage. A lower B+ voltage many extend the service life of the power tubes as well, contingent upon how hot they're biased.

HTH

Arjay

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Post subject: Re: Rectifier Tube Swapping?
Posted: Sat Feb 23, 2013 6:22 am
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aclempoppi wrote:
Thanks, Bill !!! Checked a few of my old haunts, but didn't spend enough time to get the full spec on the 5R4. Do you have the the max ma output for this tube? Didn't see any access to the specific info on the site, you provided. But I probably missed something! Art


You'll need to look up the tube data sheet for that. Maybe here:

http://www.bunkerofdoom.com/tubes/rc25/index.html

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Post subject: Re: Rectifier Tube Swapping?
Posted: Sat Feb 23, 2013 6:23 am
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Retroverbial wrote:
I don't see a problem as long as a few amp-safety protocols are observed -- namely ensuring that the power-supply's filter caps are up to the task (in the case of swapping to a higher-output rectifier) and re-biasing the tubes in the final drive stage. A lower B+ voltage many extend the service life of the power tubes as well, contingent upon how hot they're biased.

HTH

Arjay


Basically what Mike K says in the link I provided.

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Post subject: Re: Rectifier Tube Swapping?
Posted: Sat Feb 23, 2013 9:56 am
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Thanks everyone for the input. So let me see if I have this straight, say my plate voltage is 435 with a GZ34 and I go to this 5R4 then the plate volts would be more in the range of 400 or there abouts? Would this also lower the overall volume of the amp and subsequently that sweet spot that in the case of the Super Reverb from around 6-7 down to a more manageable 4-5? I will also need to rebias and check the caps or would the caps be fine considering I am moving the plate voltage down the scale vs going up?

The reason I ask is I love my BFSR but it is a bit too loud to gig with in some of the bars a band has asked me to join, so was hoping to keep my Super on duty with its great tone, but just a little less volume. Will this swap affect the tone? And am I just crazy for doing this?

T2

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Post subject: Re: Rectifier Tube Swapping?
Posted: Sat Feb 23, 2013 10:16 am
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The overall (ie: "balls-out") volume may be reduced but only marginally. And the human ear is engineered such that this nuance may be imperceptible. I think the 5R4 will lower the point at which the "sweet spot" occurs but the amp's still gonna be one loud chingalero.

JMOOC

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Post subject: Re: Rectifier Tube Swapping?
Posted: Sat Feb 23, 2013 11:29 am
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T2Stratman wrote:
Thanks everyone for the input. So let me see if I have this straight, say my plate voltage is 435 with a GZ34 and I go to this 5R4 then the plate volts would be more in the range of 400 or there abouts? Would this also lower the overall volume of the amp and subsequently that sweet spot that in the case of the Super Reverb from around 6-7 down to a more manageable 4-5? I will also need to rebias and check the caps or would the caps be fine considering I am moving the plate voltage down the scale vs going up?

The reason I ask is I love my BFSR but it is a bit too loud to gig with in some of the bars a band has asked me to join, so was hoping to keep my Super on duty with its great tone, but just a little less volume. Will this swap affect the tone? And am I just crazy for doing this?

T2


The only way to tell would be to try it. Obviously, the power tubes will need to be rebiased. Dropping the B+ voltage will also drop the voltage supply to the preamp tubes. Even though the preamp tubes are cathode biased, the biasing scheme was designed with the higher plate voltage in mind. You might find there is more tone change due to the preamp than the power amp. Whether you like the sound of that change, you'll have to decide.

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Post subject: Re: Rectifier Tube Swapping?
Posted: Sat Feb 23, 2013 4:40 pm
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T2 rock that Princeton and mic it if you have to. You will be in that sweet spot all the time.


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Post subject: Re: Rectifier Tube Swapping?
Posted: Sat Feb 23, 2013 5:41 pm
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Sorry, late to the dance. the 5R4 (as long as it's a US made one) wil work fine. It's going to have a bit more "sag" (voltage drop) than a GZ34/5AR4. Which isn't bad --- and may give the amp a more Bluesy tone.

http://www.bluestime.it/harmonica_house/amp/rect.htm

The Bendix/Cetron 5R4WGB "potato masher" is one of the toughest tube recitifers ever made.

http://tctubes.com/images/products/deta ... GB_800.JPG


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