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View Full Version : 5U4 instead of GZ34. any damage to trans


Rod Parsons
07-29-2010, 06:32 PM
Boy, I'm having a bad time with the rectifier tube in me Bandmaster Rev. I took it to a tech... he put in a 5Y3... I asked this forum about that and all agreed that that rectifier would not be up to the job... Well I thought that it was supposed to have a 5U4 in it, as I remember pulling that out of the amp long ago...the amp just sat in my closet for 19 yrs. He replaced it with a huge bottle RCA 5U4G. and I just took it out and put a thread on this sight, asking about the year, condition, etc. of this tube. But now I just also looked st the interior tube chart and see that it calls for a GZ34 rectifier..... I plaed the amp on fairly low volume with the 5U4 in it and it sounded pretty good... But as I know, the 5U4 takes more current than the GZ34..... I only played guitar and keyboard combined for maybe 2 hrs...Would that have done damage to the pwr trans. It worked fine till I turned it off and it ain't been on since... Thank you........Rod

Baxtercat
07-29-2010, 06:41 PM
Y'otta be alright.
I've been doing that in a VibroluxReverb for a while now.

Blue Strat
07-29-2010, 07:31 PM
I'm pretty sure that Bandmaster Reverbs ONLY came with 5U4GBs. I wonder if your tube chart is from another model with the same/similar tube layout. Fender is known for using any tube chart that fits even after the rectifier tube changed from a 5AR4 to a 5U4.

Prairie Dawg
07-29-2010, 10:34 PM
I'm pretty sure that Bandmaster Reverbs ONLY came with 5U4GBs. I wonder if your tube chart is from another model with the same/similar tube layout. Fender is known for using any tube chart that fits even after the rectifier tube changed from a 5AR4 to a 5U4.

as a point of information the 5u4G and GA cannot carry as much current as the 5U4GB or 5AS4. Even so the 5U4G has plenty enough muscle for your amp as a simple load analysis will show. Plus coke bottle envelopes are cool looking.

If you like the 5U4, the 5R4 will do as well and do it with less current draw, and that's always good.

Rod Parsons
07-30-2010, 07:15 AM
Thank you for all the replys..... I looked again at the tube chart and it 'does' say in big letters on the top... BANDMASTER REVERB..... and it does call for a GZ34...... I, like you, thought that the silver face amps went to the 5U4GB also...... Any way, I removed the big 5U4 coke bottle and put it in my Princeton Reverb, c. 1980....and MAN, what a difference.... I've never really played around with switching tubes around for the sake of comparing the "flavors", but the difference between the Mesa/Svetlana GZ34 that I was running in that, and the 5U4G was amazing, if not astounding.. The Princeton REALLY sounds great.... way better... STUNNING!!!!.....The Princeton Reverb does call for a 5U4, and as I calmly just stated, it do sound good. How can that be ???? Wow!! I put the Meas/ Svet GZ34, [5AR4], in the Bandmaster as I wanna be sure about the trans, being able to handle the extra one amp of the 5U4, before I find a nos one... Also ....Will the 5R4 work instead of the 5AR4.... I think I remember those being alot less expensive than nos 5AR4,[GZ34]. What's the difference??? I can't try out the Bandmaster with the GZ34 in it till my dog wakes up, ha ha!!! Again thank you Rod

tlpruitt
07-30-2010, 08:42 AM
Are you checking the bias when you switch rectifier tubes? When you switch to a different rectifier tube type a bias adjustment is usually necessary. Part of the difference you are hearing may be due to the bias being vastly different when using the different rectifier tubes.

Rod Parsons
07-30-2010, 08:57 AM
The Princeton Rev's bias is set with a specified resister, isn't it, and with the old coke bottle in it , it sounds so good, and the amp calls for the 5U4GB. If it really sounds so good, is it customary to change that bias resister to get "exact specs" instead of leaving it be... ????... And I'm still wondering if indeed the chart in the bandmaster is an old chart with "Bandmaster Reverb" printed on top, in order to use up old tube charts. And was my amp really made for a 5U4G or GB... I will be getting the Bandmstr correctly biased when I find the right rectifier tube. Thanks...Rod

Blue Strat
07-30-2010, 09:44 AM
The Princeton Rev's bias is set with a specified resister, isn't it, and with the old coke bottle in it , it sounds so good, and the amp calls for the 5U4GB. If it really sounds so good, is it customary to change that bias resister to get "exact specs" instead of leaving it be... ????... And I'm still wondering if indeed the chart in the bandmaster is an old chart with "Bandmaster Reverb" printed on top, in order to use up old tube charts. And was my amp really made for a 5U4G or GB... I will be getting the Bandmstr correctly biased when I find the right rectifier tube. Thanks...Rod


Put simply, absence of a bias pot does not relieve you of the "responsibility" to do whatever is necessary to obtain correct bias.

Old amp adage: "The best sounding amps are (often) the ones just about to blow up".

TweeDLX
07-30-2010, 11:02 AM
Also ....Will the 5R4 work instead of the 5AR4.... I think I remember those being alot less expensive than nos 5AR4,[GZ34]. What's the difference???
The 5R4 will "work", but you might want to trya 5V4 instead. Go to Blue Strat's site and read the comparison chart (http://www.kcanostubes.com/content/rectifier-comparison-and-interchangeability-chart)on rectifier tubes. That will give you more of an idea of what you're actually doing. In brief, you change the voltage with each swap. Always rebias when you do, unless you like spending lots of money on tubes and repairs... :)

Mike

Prairie Dawg
07-30-2010, 01:43 PM
The 5R4 will "work", but you might want to trya 5V4 instead. Go to Blue Strat's site and read the comparison chart (http://www.kcanostubes.com/content/rectifier-comparison-and-interchangeability-chart)on rectifier tubes. That will give you more of an idea of what you're actually doing. In brief, you change the voltage with each swap. Always rebias when you do, unless you like spending lots of money on tubes and repairs... :)

Mike

The nice thing about the 5T base platform is that there are a number of good choices that you can use to adjust your plate voltage up or down a bit and the 5V4 is one of them. It's indirectly heated like the 5AR4. Having said that, my preference runs to the older coke bottle style 5V4s because the newer short bottle numbers seem to make more noise than is desirable. The 5R4 is a better choice than the 5V4 if you want the lower plate voltage that a 5U4 will yield-all things being equal of course-and you want to lighten the load a bit on the power transformer.

So no, it doesn't "work" because there's sort of a negative connotation there-the unspoken "but". It operates properly and does a good job where its operating characteristics are desirable. The only drawback is that some people end up trying to put Chatham (Cetron) potato masher 5R4s into places where they don't fit without surgery.

Rod Parsons
07-30-2010, 02:04 PM
Thank you bluestrat for the "It's probably an old tube chart", as I found that you are right!!!! All of the Bandmstr Rev.'s run on 5U4- GB's.. I'm very happy about that, especilly because I didn't hurt the amp, and just as importantly, I can get really great 5U4's alot cheaper. aaaaaAlso I tried to email a letter to kcanostubes@verizon.com , as I read that this was a sight either owned or recommended by you... My computer sent back a message that something was wrong with the recipient's address or something.... anyway, if you read this, please let me know how to do it... new address ??? Thanks to all of you who have advised me, also. You are all right... Rod

davemccarthy707
07-30-2010, 02:16 PM
I am going to make a bold statement here about Fenders. The 5U4GB will function properly in any Fender amp calling for a 5AR4 as long as the power transformers are the same part number. IE the 1970 super reverb calls for a 5u4gb and has the same power transformer as a 1967 Super reverb that uses a 5AR4. The part numbers are identical.

-Dave

Blue Strat
07-30-2010, 02:22 PM
Thank you bluestrat for the "It's probably an old tube chart", as I found that you are right!!!! All of the Bandmstr Rev.'s run on 5U4- GB's.. I'm very happy about that, especilly because I didn't hurt the amp, and just as importantly, I can get really great 5U4's alot cheaper. aaaaaAlso I tried to email a letter to kcanostubes@verizon.com , as I read that this was a sight either owned or recommended by you... My computer sent back a message that something was wrong with the recipient's address or something.... anyway, if you read this, please let me know how to do it... new address ??? Thanks to all of you who have advised me, also. You are all right... Rod


The address is kcanostubes@verizon.net not .com ;)

PS, Schematicheaven.com DOES show a Bandmaster Reverb schematic with a GZ34 so I'm not sure what is actually correct. Manufacturers don't purposely design components with no margin (that will blow up if you exceed nominal specs by 10%), but the 5U4 presents a 50% higher load than a 5AR4/GZ34 or 5R4 (which will perform more like a 5U4 without the current draw, and is cheaper than both of the other options).

Rod Parsons
07-30-2010, 06:31 PM
Thanks, Blue Strat and Baxtercat..... That's a good point about comparing the pwr. trans to codes of another with the 5U4 designation.... And I'm so glad that I got the answer about the 5AR4 and the 5R4, because I saw that they are alot cheaper, and I loved the 5U4G sound that I had with the ST RCA . So if I can find the trans code #, and if the 5U4 will work, than I will have the best of both worlds... by the way..... I do have that large 5U4 in my Princeton Reverb, [1980],and before I was using a "Mesa / Svetlana GZ34 / 5AR4...And since the 5U4 puts out a little "less" than a 5AR4, wouldn't that mean that there is actually less chance of making the tubes idle hotter ??? ...... That old big bottle sounds so huge in the Princeton, that I hate to have to get the bias set differently. The 5AR4 was in there for about 3 years, however it was very light duty usage...and I have never had the bias checked since I got it in 1981. I'm definately going to get a 5R4.... Thanks for the correct email, Blue Strat...... with respect,...... Rod .....

zombiwoof
08-01-2010, 11:59 PM
The nice thing about the 5T base platform is that there are a number of good choices that you can use to adjust your plate voltage up or down a bit and the 5V4 is one of them. It's indirectly heated like the 5AR4. Having said that, my preference runs to the older coke bottle style 5V4s because the newer short bottle numbers seem to make more noise than is desirable. The 5R4 is a better choice than the 5V4 if you want the lower plate voltage that a 5U4 will yield-all things being equal of course-and you want to lighten the load a bit on the power transformer.

So no, it doesn't "work" because there's sort of a negative connotation there-the unspoken "but". It operates properly and does a good job where its operating characteristics are desirable. The only drawback is that some people end up trying to put Chatham (Cetron) potato masher 5R4s into places where they don't fit without surgery.

I recently suggested using a 5V4 in a Fender, and Bluestrat basically suggested that you might blow up your amp doing that. I've been using one in my '65 PR for some time with no problems, so I was surprised about that. Interesting that he hasn't jumped in on this discussion.

Al

Blue Strat
08-02-2010, 06:02 AM
I recently suggested using a 5V4 in a Fender, and Bluestrat basically suggested that you might blow up your amp doing that. I've been using one in my '65 PR for some time with no problems, so I was surprised about that. Interesting that he hasn't jumped in on this discussion.

Al


I don't remember that. The only time I would recommend caution is when moving from a 5Y3 in a 6V6 (increased plate voltage) amp though you might also hit the max forward current of a 5V4 in a 6L6 amp. Every situation is different and measurements have to be taken. I'd rather err on the side of caution when someone elses amp is at stake.

zombiwoof
08-02-2010, 12:23 PM
I don't remember that. The only time I would recommend caution is when moving from a 5Y3 in a 6V6 (increased plate voltage) amp though you might also hit the max forward current of a 5V4 in a 6L6 amp. Every situation is different and measurements have to be taken. I'd rather err on the side of caution when someone elses amp is at stake.

http://www.thegearpage.net/board/showthread.php?t=749658

After re-reading your response, you may have meant destruction to the tube, and not the amp (this is unclear to me, I asked you to elaborate but I guess you never saw my question). But you basically shot down my suggestion to sub a 5V4 for a 5AR4.

Al

Blue Strat
08-02-2010, 12:37 PM
http://www.thegearpage.net/board/showthread.php?t=749658

After re-reading your response, you may have meant destruction to the tube, and not the amp (this is unclear to me, I asked you to elaborate but I guess you never saw my question). But you basically shot down my suggestion to sub a 5V4 for a 5AR4.

Al


EVERY SITUATION IS DIFFERENT. I don't know how else to say this.

Check the spec on the component (Google 5V4GA data), look for the maximum forward current, figure out or measure how much the maximum current (for KT66s in the original example) a pair of power tubes will pull from the power supply (plus everything else in the amp) and make a decision. 5V4's can't supply/pass as much current as a 5AR4.

My point was that without doing this analysis YOU DON'T KNOW...and to blindly make a recommendation based on no data is irresponsible.

The most danger posed is to the rectifier but when something blows there's always the possibility of collateral damage.

dudleys100
12-16-2010, 08:55 AM
I know this is an old thread but the Bandmaster reverb did use the GZ34 in its first circuit design used in 68 (maybe for some of 69 too). I have a 68 and it still has the stock GZ34 along with 60's RCA 6L6's. Mine also has the drip edge front.