Started a Rowe R-4359A amp conversion

Bill, very nice! I hope you're as happy with the sound of yours as I was with mine. Ya know, Bob Carver sells a version of this amp that, according to him, has incredible specs in the power, distortion, and frequency areas. Of course, I can't verify any of his numbers, and won't repeat them. BUT, I can say that I've had mine running for about 2 years now......and I'm as delighted with it's sound today as I was when I first got it running. And, no problems with it in any way. So..... pretty 'reliable' as well. WC
 
Congrats on a successful and beautiful build. The handle(s?) and tube guard are nice touches.
 
Well I have some issues, but can still hear a lot of potential as well, the bass is increadable and power is no problem. The bad, random squealing from tubes and a definite hum in both channels. So far tried cleaning the tube sockets, backing off bias, but no joy. Noticed all tubes are a little harmonic if tapped, and one is bad, that one can't seem to keep a stable bias like the others. I tried quite diligently to follow a single bus ground with stages kept together. I also had done a pretty good job of twisting up the heater wires but had to redo both 12ax7 heater lines due to my stupidly miswiring them, forgot they had a pin 9, So I lost a little ground there.
 
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Sorting old tubes can be as challenging as the rest of the amp. But, glad you found 'the culprit'! I spent some time tonight listening to my Rowe 'shop' amp.....and still get impressed every time I do. But, being 3 am now..... I'm just going to confine my comment to 'glad it's working', and 'give an update as soon as you replace the guilty party!'. WC
 
Since one of the biggest benefits of this forum is the wealth of knowledge it provides and one of the best means is through learning from others trials and tribulations, I will document my failings as I work my way through my excessive hum elimination journey.

I have removed (temporarily maybe) the power cord ground, which dropped the hum by 50%, but still too loud.

I pulled both driver tubes, and the hum was almost negligible (as would be expected).

I then installed two different 12AX7 tubes. No improvement.

I redressed the heater wiring to the drive tubes and moved the 6.3v connection over to the first output tube instead of to the driver tubes first. No improvement.

Installed a virtual tap w/ two 100 ohm resisters. Very small improvement.

Next up I am installing a humdinger pot, next then raise the heater level up with DC, as last resort I will add a DC circuit of some kind, just for the two driver tube heaters.

Question, I see a lot of mention of using cathode voltage to raise the heater level up with, and that about 70v - 80v is typical. My output tube cathodes are at ground level, so should I use the B+1 @ 250v, and do I need to drop it to this 80v level, or can I leave it at the 250v level? Or should I take it off of B+ and divide it down? if so to what voltage level?
 
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Well upon further investigation it seems the virtual tap was a waste, it is center tapped already. Also to float the heater circuit I can use B+ and a voltage divider and cap.
 
Bill,

Just a quick comment here as I'm really just 'passin' through' on my computer. But, I'll say that my Rowe conversions..... in fact all of them, have been dead quiet. I did have a problem, but I found it to be my input inter-connects. I also had a problem and it turned out to be the pre-amp itself. Basically I made up a set of 'grounded' RCA jacks and I plugged 'em in. I get very little noise with nothing plugged into the input plugs...but with the 'grounded' jacks plugged in I'd call my amps 'noiseless'. I honestly hear nothing coming from them. I went through a couple of pre-amps, and several sets of interconnect cables....... I even did a thread on the subject of interconnects as I found that some of my more expensive sets induced more noise than some of the cheap versions. Ultimately I ended up with an old Kenwood SS pre-amp driving an old 'Denon' CD player and into the Rowe amp and on to my Cornwall speakers. When working either on a motorcycle or on the bench on any project, I'm only several feet away from the speakers.....and believe me, if there was ANY noise at all, I'd hear it!! I consider myself VERY sensitive to that. So, my point is that the design of the amp itself is not inherently prone to this problem. As such, redesigning the whole filament scheme seems a bit unnecessary to me.... but it's your call. I just hate to see you go through all that and find it's something simple. Did you plug in a 'grounded' set of cables to check to see if hum was coming from outside the amp? Tom D.
 
I have not, but I will. I have about 20db of 60Hz hum. With my efficient speakers its crazy loud to me. I figured you were not hearing that kind of hum, or would mention it. My preamp doesn't cause me any trouble with my other tube amp, though it could be different. Does your amp have hum pots, this one does not.
 
My amp is basically built EXACTLY to the ORIGINAL Rowe schematic...... with the removal of ALL superfluous Juke Box 'stuff'......and the addition of a pot in the bias circuit so I could 'adjust' the overall bias voltage. I also added 10 ohm resistors to ground off the Cathodes of each power tube and, as I said, I used the 70V speaker connections as 'test points' to measure each tube. Though I do NOT have an IBAM, I am able to measure the bias current draw of each tube and assure that I'm running a reasonably well matched quad set. I can 'adjust' the bias supply voltage, so I'm able to get my amps tubes to all be at about 38ma of current draw give or take a couple of ma. All but one of my 're-furbs' still have the original 'input' locations for the RCA jacks, but even the one I completely re-did (in my avatar picture).....that has no associated hum problems. I might add one last thing: I did a 'Hum Fighters Unite!!' thread some time back.....just because of the frustration of chasing the elusive 'hum' bandit throughout an amp. Had some good posts in it.....so may be worth a read if you decide to go through it. But trust me, I feel your pain! I've had MANY amps that have had hum problems with no apparent cause! VERY frustrating!!!

Bad storms here tonight! Had some household flooding! Damn! Too cold.... too hot, too dry, too wet.... Always 'too something'! Where can one go where you have the 'perfect' weather for the race? (that would be the 'human race'....lol). WC
 
I will definitely read that hum fighters thread. I know this hum thing is a nuisance, I feel for you with you're flooding, that is way more than just a little hobby nuisance. Hopefully it will cut you some slack over the next few days. I will keep everyone posted here on my progress, and especially good luck to you. Thanks.

My amp is basically built EXACTLY to the ORIGINAL Rowe schematic...... with the removal of ALL superfluous Juke Box 'stuff'......and the addition of a pot in the bias circuit so I could 'adjust' the overall bias voltage. I also added 10 ohm resistors to ground off the Cathodes of each power tube and, as I said, I used the 70V speaker connections as 'test points' to measure each tube. Though I do NOT have an IBAM, I am able to measure the bias current draw of each tube and assure that I'm running a reasonably well matched quad set. I can 'adjust' the bias supply voltage, so I'm able to get my amps tubes to all be at about 38ma of current draw give or take a couple of ma. All but one of my 're-furbs' still have the original 'input' locations for the RCA jacks, but even the one I completely re-did (in my avatar picture).....that has no associated hum problems. I might add one last thing: I did a 'Hum Fighters Unite!!' thread some time back.....just because of the frustration of chasing the elusive 'hum' bandit throughout an amp. Had some good posts in it.....so may be worth a read if you decide to go through it. But trust me, I feel your pain! I've had MANY amps that have had hum problems with no apparent cause! VERY frustrating!!!

Bad storms here tonight! Had some household flooding! Damn! Too cold.... too hot, too dry, too wet.... Always 'too something'! Where can one go where you have the 'perfect' weather for the race? (that would be the 'human race'....lol). WC
 
This has become a virtual odyssey in a tube audio kind of way. Of course we learn best from failure, or a least learn for much longer, hence odyssey. So let's commence shall we?

Since my last update, I have ...
tried plugging it into a different source and pre-amp, no joy.

re-routed and twisted the driver tube heater wires for the 4th time.

identified the 6.4V center tap, built a voltage divider and lifted the heater circuit about 50vdc. I immediately thought that had caused the wire to the on/off switch to start smoking and melting. So I fixed the overheated wires, checked over every inch of the lift divider circuit, though one solder joint seemed a little wonky and reflowed it, everything else checked good, so tried it again, hot wires. At this point I knew what I had to do, I cut out the whole lift voltage divider circuit, the way god had intended it by the way, turned it back on, the heater wires to the output tubes start smoking. As it turns out clear back at the start I chose to use some questionable radioshack solid wire with plastic insulation (I hate that stuff by the way) and two heater wires had shorted at one of the tight twists, likely due to a passing hot solder iron, because I didn't feel the output tubes were causing the issue and the wiring on some of them was really nicely done, and I get tired of rewiring tube sockets, you know I hadn't changed all of them. So now I have, I used expensive teflon oxygen free Kimber stranded wire @ some god awful amount /ft, because thats all I had. I live in a little town in the middle of no where. I have put everything back together, cleaned it all up and guess what? Yep 60hz HUM. You didn't think I was going to say it was quiet did you? How would that be an odyssey?

So, it is sitting next to me on the dining room table playing white noise into my test speakers at full volume while I think, and type this out for you as a warning. I can't hear the HUM over the white noise at full volume. Hey is that a valid repair?

Next I will try ...
1. Humdinger pot.
2. Trash can.
 
Well, one good thing, my faith in humanity is restored a little, 999 views and no one has tried to convince me I need a $320 capacitor to improve the sound of my Hum.

I think this thing is throwing off my rhythm.
 
Can you post a high resolution picture of the underside so we can try look for small details? Hum can be a bugger, but it CAN be worked. I don't have extremely high sensitivity speakers, 93dB is the highest, so a small bit of hum doesn't bother me. I also have zero or low feedback amps and getting that last bit is tougher but it can be done. Maybe a $300 capacitor would help, not sure as I've never had one.

Never give up, never surrender. (Galaxy Quest, a great movie)
John
 
I can take a high resolution photo and post it, I actually have been thinking long and hard about digging the ole camera out and getting back into photography recently. It's a relaxing civilized hobby.
 
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Between the Blue 80uF cap and the bottom of the transformer is where all of the heater lines run from in paralles. Previously I had routed them all as one long parallel socket to socket run, but could not avoid direct contact with input signal wires or bias wires. This way I ran the two driver tube lines separate and direct to tube socket (green twisted), the output tubes remain socket to socket via the (red/black twisted), (the expensive) wires. This allowed the most direct to the heater pins, and trust me when I say I tried many other routings without any better results.

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The right channel side.

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Left channel side

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Backside of left driver socket.

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Close up of a output tube socket which is wired socket to socket in parallel. Without any driver tubes installed the amp is relatively quiet, that is why I have been focusing on the driver sockets and heaters to them. Ground is a single bus only attached at mounting bolt of power transformer and chassis. All other grounds either are stared together (driver section) at input ground (isolated from chassis) and then power and output section straight to bus. Chassis is attached to ground of power but I have a two prong adaptor on it as the noise floor goes up if used. I have one bad output tube (harmonic but works), tried all new 12AX7 driver tubes with no benefit. Transformers all remain between cool to touch (output) and just warm (power). If you can look at these and tell me how to fix, you get a big Gold Star and a God Bless you.
 
Have you tried isolating the ground bus from the chassis? Are you using a 3-wire power cord? I see you have a chassis connection at the AC socket and the ground bus looks to be connected to chassis at the power supply end.
 
I have the ground bus attached only to the transformer mounting bolt using star washers on the caticorner post from the one the power cord is attached to. Are you suggesting I isolate the bus from the chassis all together? I tried following one persons advice and split the ground bus between power supply section and amp section and then couple them via a .047 uF cap, this left the hum intact and made the sound all off in frequency. I now have to jumper my nice solid bus wire. What will be the difference in isolating the bus than from using the cheater plug which removes the ground pin for the cord?
 
Have you already tried a cheater plug? I must have missed that in the discussion. A cheater plug will tell you if you have a ground loop with other gear in the system. If the cheater plug quiets the hum, you can leave the ground bus isolated from the chassis, or use a hum breaker with diodes and caps to give some isolation but still provide a ground path in case of a short circuit.

Look at this article and see the ground loop breaker about 2/3 down the page. There are other versions on the web. I've sometimes used just a power resistor of 1-2 ohms between signal common and chassis AC ground.
http://sound.westhost.com/earthing.htm

John
 
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