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    Rectifier substitution for M-125

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    buchela

    Posts : 30
    Join date : 2011-03-09

    Rectifier substitution for M-125

    Post by buchela on Sun May 15, 2016 12:36 pm

    I've been running my M-125 with the Webers WZ68, recently I've been using 5AR4 rectifiers, but that makes me bring the bias down and I don't like the consecuence. So I tried to get the GZ33 bottle but  CHEESE WHEESE THEY ARE SCARCE AND EXPENSIVE.
    So I've been thinking about the possibility of using two 5AR4 rectifiers insted of weber WZ68, is this a bad idea ?
    Are two of these 5AR4 equal to one WZ68 ?. or which two tube rectifiers  ( if any ) are equal to one WZ68 ? .
    Any advice will be greatly appreciated

    sKiZo

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    Join date : 2013-04-01
    Location : Michigan USA

    Re: Rectifier substitution for M-125

    Post by sKiZo on Sun May 15, 2016 2:05 pm

    Your timing is impeccable ... This was just posted.

    "You can use a 5V3 as a rectifier in any of the VTA amps"

    http://dynacotubeaudio.forumotion.com/t3036-direct-vs-indirect-heated-rectifiers-in-st120#26424

    Quick peek at that auction site shows a nice selection for around $20 or so.

    buchela

    Posts : 30
    Join date : 2011-03-09

    Re: Rectifier substitution for M-125

    Post by buchela on Sun May 15, 2016 4:22 pm

    Thanks Skizo. I am looking into the feasibility of using two tube rectifiers in the same M-125 monoblock that I can bias as high ( 1.2A ) as the weber WZ68. I would have to make another hole on the chasis or an adapter with twin sockets on top of the existing rectifier socket; which I prefer because if I do not like how they treat my music I can unplug it and forget about. ( I am making another chassis with more real state )



    Last edited by Bob Latino on Sun May 15, 2016 6:58 pm; edited 3 times in total (Reason for editing : corrected phrasing)

    sKiZo

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    Re: Rectifier substitution for M-125

    Post by sKiZo on Sun May 15, 2016 4:28 pm

    Got room to relocate the quad cap underneath? That would free up that spot up top and maintain symmetry and proximity.

    Here it is on my ST120 ... custom case though, so lots of room.



    Not sure what the 5V3 would allow for bias without stressing anything as it's known to produce a slightly lower B+ on these amps ...

    buchela

    Posts : 30
    Join date : 2011-03-09

    Re: Rectifier substitution for M-125

    Post by buchela on Sun May 15, 2016 4:41 pm

    Great idea !!!!!, my quad caps are going "down".
    Your chassis is full of very useful ideas. Thanks sKiZo

    Tubes4ever

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    Join date : 2015-07-14
    Location : Star, Idaho

    Re: Rectifier substitution for M-125

    Post by Tubes4ever on Sun May 15, 2016 6:03 pm

    buchela wrote:Thanks Skizo. I am looking into the feasibility of using two tube rectifiers in the same M-125 monoblock that I can bias as high ( 1.2A ) as the weber WZ68. I would have to make another hole on the chasis or an adapter with twin sockets on top of the existing rectifier socket; which I prefer because if I do not like how they treat my music I can unplug it and forget about. ( I am making another chassis with more real state )

    Pardon me if I missed something here, but what could you possibly need 1.2 AMPS of total current flow for the power tubes on your mono blocks? Just how hot do you run your tubes?
    Not criticizing, just curious.

    Tim

    buchela

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    Re: Rectifier substitution for M-125

    Post by buchela on Sun May 15, 2016 6:39 pm

    That is the recomended setting for the Webers WZ68 with four kKT88 tubes

    Bob Latino
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    Re: Rectifier substitution for M-125

    Post by Bob Latino on Sun May 15, 2016 6:59 pm

    buchela wrote:Thanks Skizo. I am looking into the feasibility of using two tube rectifiers in the same M-125 monoblock that I can bias as high ( 1.2A ) as the weber WZ68. I would have to make another hole on the chasis or an adapter with twin sockets on top of the existing rectifier socket; which I prefer because if I do not like how they treat my music I can unplug it and forget about. ( I am making another chassis with more real state )


    You are not biasing at 1.2 amps .. You are biasing at 1.2 VOLTS DC per each side in the 4 output tube mode of operation. This gives a bias current of 60 milliamps per each output tube.

    Bob

    sKiZo

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    Re: Rectifier substitution for M-125

    Post by sKiZo on Sun May 15, 2016 7:11 pm

    In any case, that would tend to stress an average 5AR4 ...

    And yes, good to know the difference between amps and volts, said the curly headed chap with glowing eyes and blisters on his fingers ...

    buchela

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    Re: Rectifier substitution for M-125

    Post by buchela on Sun May 15, 2016 7:59 pm

    Thanks for the correction Bob, I believe you have stated this a few times in the past

    Tubes4ever

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    Re: Rectifier substitution for M-125

    Post by Tubes4ever on Sun May 15, 2016 8:56 pm

    buchela,

    Now that we've got amps and volts straightened out Wink

    As Skizo noted, the 5V3 would be a good replacement. It can easily handle the 240mA of current. It can easily handle 350mA for that matter.

    buchela

    Posts : 30
    Join date : 2011-03-09

    Re: Rectifier substitution for M-125

    Post by buchela on Mon May 16, 2016 8:46 am

    Thanks Tubes4 ever,I am trying to stay away from NOS/hard to get tubes unless I have a pile of them, I don't see many 5V3, the ones I have seen look like they were picked up from the dumpster, although I see a couple of variants of it, but I'm not very knowledgeable in this field, as you may have realized already.

    Tubes4ever

    Posts : 61
    Join date : 2015-07-14
    Location : Star, Idaho

    Re: Rectifier substitution for M-125

    Post by Tubes4ever on Mon May 16, 2016 10:00 am

    buchela,

    If you want a current production tube then go with a 5U4GB. It is rated for 275mA and can handle your current requirements with out stress. The 5V3 was suggested because it can handle even more current and is relatively cheap and easy to get.

    buchela

    Posts : 30
    Join date : 2011-03-09

    Re: Rectifier substitution for M-125

    Post by buchela on Mon May 16, 2016 10:56 am

    I found some 5V3A, but I assumed it was a variant of 5V3, and didn't know if it could handle as much as Weber WZ68. But you just put me on solid ground, I very much appreciate your help

    sKiZo

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    Re: Rectifier substitution for M-125

    Post by sKiZo on Mon May 16, 2016 1:17 pm

    I'm probably reading the data sheet wrong, but it looks like the 5V3A can put out 400+ mA BUT with a corresponding high load on the iron. Maybe too high?

    http://www.nj7p.org/Tubes/PDFs/Frank/049-RCA_Cuningham/5V3A.pdf

    Tubes4ever

    Posts : 61
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    Location : Star, Idaho

    Re: Rectifier substitution for M-125

    Post by Tubes4ever on Mon May 16, 2016 1:30 pm

    Skizo,

    The 5V3 pulls 3.8 amps heater current and the 5V3A pulls 3.0 amps, same as 5u4GB.

    Bob L. says that either one will work just fine because the 5V winding is rated at 4 amps on a ST70. I don't know what the 125 mono block is rated at, but it is at least 4 amps. So, there is no issue with using either one.

    Bob, what is the 125 5V winding rated at?

    sKiZo

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    Location : Michigan USA

    Re: Rectifier substitution for M-125

    Post by sKiZo on Mon May 16, 2016 1:34 pm

    Thanx! I've added that info to my vast suppository of knowledge here ...

    Tubes4ever

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    Location : Star, Idaho

    Re: Rectifier substitution for M-125

    Post by Tubes4ever on Mon May 16, 2016 1:40 pm

    buchela wrote:I found some 5V3A,  but I assumed it was a variant of 5V3, and didn't know if it could handle as much as Weber WZ68. But you just put me on solid ground, I very much appreciate your help

    Go with the 5V3A if you can get one.  It will be easier on your power transformer 5V winding...less heat.

    It is a variant of the 5V3. The "A" version uses less heater current.


    Last edited by Tubes4ever on Mon May 16, 2016 1:42 pm; edited 1 time in total (Reason for editing : More info)

    buchela

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    Join date : 2011-03-09

    Re: Rectifier substitution for M-125

    Post by buchela on Mon May 16, 2016 11:46 pm

    I've just got a couple of decent 5V3, and a shedload of 5U4GB as a backup. You are correct 5V3As are even harder to find. Finally I will find out what type of rectification sounds better to my ears, and/or whether or not I can detect any audible difference between solid state and tube rectification, all things being equal. ( M125 monoblocks ).Thanks Tubes4ever, thanks sKiZo

    BNR_1

    Posts : 78
    Join date : 2013-06-11

    Re: Rectifier substitution for M-125

    Post by BNR_1 on Tue May 17, 2016 4:14 pm

    Can anyone comment on the SQ of using the 5V3A in the M125 amps? If the volume is loud and everything else is equal does the sag affect the SQ?

    I am curious if there are any noticeable differences with using a NOS/OS 5V3A vs NOS/OS Mullard 5AR4 in a 2 tube or 4 power tube configuration (KT-120 or 88) & loud vs mild to low volume levels.

    Bottom line - I am curious about the level of sag and the effect (if any) it has on the SQ with using the 5V3A tube. If there are none to minimal effect on SQ then the use of the 5V3A can be a big savings vs. the NOS/OS Mullard 5AR4....(assume PT can handle the extra current draw which the M125 is design for).

    bluemeanies

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    Re: Rectifier substitution for M-125

    Post by bluemeanies on Thu May 19, 2016 6:57 pm

    This won't answer your question but I recently purchased a pair of Mullard GZ33's (GREAT PRICE) that I intend to use with my m125's with a four Output tube configuration.
    I have the Sovtek KT88's but I was told these Mullards can handle four KT120's without braking a sweat.
    By no means am I an expert and this is not a wise crack but I never heard of using TWO rectifier tubes in the m125's.
    Can it be done without any retro fitting or re-wiring?
    Just curious.

    stewdan

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    Location : Houston Texas

    Re: Rectifier substitution for M-125

    Post by stewdan on Thu May 19, 2016 8:29 pm

    Blu ---- using two rectifiers (two 5V3's or 5V3A's, two GZ34's, two GZ37's or two GZ33's) means wiring the 2nd rectifier in parallel to the 1st rectifier. Where there is wire attached to socket pin-X on rectifier #1, you would run a wire from there to the corresponding socket pin-X on the 2nd rectifier.

    This in parallel wiring, effectively doubles the mA current output for the pair of rectifiers. So, if 1 rectifier could output 400 mA, the pair could output 800 mA of current.

    You would need a 2nd hole for the 2nd rectifier or you could move the Quad Cap underneath the chassis and use its hole for the 2nd rectifier. You would also need a tube socket and mounting hardware for the 2nd Rectifier.


    bluemeanies

    Posts : 129
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    Re: Rectifier substitution for M-125

    Post by bluemeanies on Thu May 19, 2016 8:34 pm

    stewdan wrote:Blu ---- using two rectifiers (two 5V3's or 5V3A's, two GZ34's, two GZ37's or two GZ33's) means wiring the 2nd rectifier in parallel to the 1st rectifier.  Where there is wire attached to socket pin-X on rectifier #1, you would run a wire from there to the corresponding socket pin-X on the 2nd rectifier.  

    This in parallel wiring, effectively doubles the mA current output for the pair of rectifiers. So, if 1 rectifier could output 400 mA, the pair could output 800 mA of current.

    You would need a 2nd hole for the 2nd rectifier or you could move the Quad Cap underneath the chassis and use its hole for the 2nd rectifier.  You would also need a tube socket and mounting hardware for the 2nd Rectifier.



    Thanks Stewdan for the explanation!
    Have you experienced the m125 with two rectifier tubes?
    If so, what as your thoughts?

    Tubes4ever

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    Join date : 2015-07-14
    Location : Star, Idaho

    Re: Rectifier substitution for M-125

    Post by Tubes4ever on Thu May 19, 2016 10:31 pm

    Keep in mind that the 5V winding will have to provide at least 6 amps of current. I don't think the m125 transformer is designed to put out that much.

    stewdan

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    Two Rectifiers

    Post by stewdan on Thu May 19, 2016 11:02 pm

    Hi Blu --- The only 2 rectifier configuration that I have used was two GZ34's on an upgraded ST-70 amplifier about 20 years ago. I used a cap board underneath the chassis and reamed out the chassis hole where the quad cap originally was and put the 2nd rectifier there.

    I have a pair of M125's and use the GZ37 rectifier (one per chassis). I use GZ34's everywhere else.

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