Heathkit W-5M done! Bass Balance question

[Steve O]

Perhaps we should start a new thread?..or these posts about the W4 moved to a new thread? Any moderators watching this?

Also, Gordon, be sure your plate feedback cap is rated for at least 1000V for a little margin, 500V caps won't do. Silver micas are the best (and also the most expensive), but ceramics will do as well.
good luck,:thmbsp: let us know how it turns out.

Actually, the 1KV cap rating I noted is absolute minimum w/o margin. 20W across 10K ohm = 630V peak + 375DC = 1KV. Although I used 1KV cap, if I were to sell this with the mods, I'd replace the cap with a 1.6 or 2KV part.

[Edit]
Oops...Above is incorrect. Failed to account for centertap primary. Should be 20W across 10K ohm ~450VRMS. 1/2 this appears betw either plate and CT so peak V betw plate and ground =225*1.414 + B+. Meas B+ = 420VDC so peak V = 318+420 = 738V. Regardless, I'd still go for a 1.6KV cap.

 

[GordonW]

Also, Gordon, be sure your plate feedback cap is rated for at least 1000V for a little margin, 500V caps won't do. Silver micas are the best (and also the most expensive), but ceramics will do as well.
good luck,:thmbsp: let us know how it turns out.

Right, this I figured... possible inductive spikes and such, well beyond the PS voltage.

Been looking for silver-micas, but may wind up using a ceramic, just because of being able to easily get the 1KV rating. Will probably look for 1.2K or 1.4K rating... those are usually fairly easy to find.

I'm guessing, that since these caps are acting pretty much outside the "audible" audio bandwidth, that using a ceramic cap here isn't the end of the world. Heck, the ceramic caps in the feedback loop of my Eico HF22s are still there, and nobody faults the sound of THAT amp AT ALL... it's astoundingly good!

Regards,
Gordon.

 

[bricktop]

Actually, the 1KV cap rating I noted is absolute minimum w/o margin. 20W across 10K ohm = 630V peak + 375DC = 1KV. Although I used 1KV cap, if I were to sell this with the mods, I'd replace the cap with a 1.6 or 2KV part.

Since the turns ratio from supply to each plate is equal, and a tube that drives a plate winding full to ground (though this never happens) will develop the full B+ across across the other (at AC). If the B+ is 420, which is what I think I recall I measured once (yours may vary), 420VDC+420VACpeak = 840V max on a plate.

With your Ra-a=10k, B+=375 primary example, you have to take half of the AC peak since it is center tapped, so 630/2+375=690Volts (peak). The 690 is more like what it will see, since 20W is pretty loud (on decent speakers), but I looked at worse case (i.e. if an output tube suddenly shorts).

So, unless the B+ is greater than 450VDC, a 1kV cap is mostly fine. But, like you said, if I were to sell something, I would use a higher rated cap as well, but I'm the cautious type, and I think Murphy hates me

 

[Steve O]

Since the turns ratio from supply to each plate is equal, and a tube that drives a plate winding full to ground (though this never happens) will develop the full B+ across across the other (at AC). If the B+ is 420, which is what I think I recall I measured once (yours may vary), 420VDC+420VACpeak = 840V max on a plate.

With your Ra-a=10k, B+=375 primary example, you have to take half of the AC peak since it is center tapped, so 630/2+375=690Volts (peak). The 690 is more like what it will see, since 20W is pretty loud (on decent speakers), but I looked at worse case (i.e. if an output tube suddenly shorts).

So, unless the B+ is greater than 450VDC, a 1kV cap is mostly fine. But, like you said, if I were to sell something, I would use a higher rated cap as well, but I'm the cautious type, and I think Murphy hates me

Oops...You're absolutely correct about the relative magnitude of the voltage. I forgot to account for the fact that the OPT is centertapped. I got to thinking about this just after I hit the submit button and decided to make some actual meas before anybody noticed...but you were too quick for me.

Anyways, based on the correct analysis, what we have is 20W across the full 10K winding ~450VRMS or 1/2 that across either side of CT = 225RMS. Peak voltage above ground will then be 225*sqrt(2) + B+. I just measured the B+ on my W4 and although the schematic says it should be 375VDC it's actually 420 as you remember. ACV betw CT and either plate also meas ~225V @20W out confirming assumptions. So, plugging this all in we get 225*1.414 + 420 = 738V peak. So a 1KV cap is probably OK. But I'd still put on a higher voltage cap if I were going to sell this.

I'm going to go back and correct my previous post but you've quoted me for posterity so I don't get off w/o some egg on my face.

 

[DaWoofer]

You gentlemen sure give a W-4 newbie a whole bunch of possibilities to ponder besides just the normal recap job. As soon as I can afford a signal generator or injector I will experiment and hopefully be able to give my personal input on some of these mods. The links and your men's input have really raised to bar to the normal upgrade. Sure sounds like I have much fun planned for the future. Got to sell some stuff off, I'm anxious to get going.

 

[k**rkleclaire]

Steve-O, Mission accomplished! I transplanted the "Junker" OP , got the tubes to balance and for now all seems well. Thank you for all your help.

 

[k**rkleclaire]

Whoa.. Stevo-O.Yesterday after I replaced the Op everthing was working well. Today I went to re balance the tubes and they won't balance, when the pot spins to the far side my multi meter beeps indicating continuity this can't be good. I also tested the power plug for continuity. yes it beeps, there is continuity in that also.9 Just to be safe i replaced that) Could this be the Power Transformer? I checked all the posts on all the tube sockets and they are near 25% of spec.(no change since yesterday) Do you have any thoughts on what I should do. the amp is still working.I don't want to ruin it.Should i get an after market Power tranny and OP transformer and be done with it?
Kirk

 

[k**rkleclaire]

Steve-O ignore the previous post, a bit of insanity from a novice. I thought there was a problem where none existed!!!! Then I broke a tube base....oh well, I'm going to monitor the Transplanted OP....If that goes south I'm sure i'll need some advice.
Again thanks for your patience,
kirk

 

[Steve O]

Whoa.. Stevo-O.Yesterday after I replaced the Op everthing was working well. Today I went to re balance the tubes and they won't balance, when the pot spins to the far side my multi meter beeps indicating continuity this can't be good. I also tested the power plug for continuity. yes it beeps, there is continuity in that also.9 Just to be safe i replaced that) Could this be the Power Transformer? I checked all the posts on all the tube sockets and they are near 25% of spec.(no change since yesterday) Do you have any thoughts on what I should do. the amp is still working.I don't want to ruin it.Should i get an after market Power tranny and OP transformer and be done with it?Kirk

Kirk:

When making the balance adj, your multi-meter should be in the DC volts mode and probably at the most sensitive range. I know of no meter that indicates continuity in the volt mode but many do in the resistance (ohms) mode. Are you sure you're in the right mode when making this measurement???

Regarding transformers, if I understand the story correctly so far, you're using a replacement PT and an OEM Peerless OPT (which one, 458 or 309??). Since the amp is working OK at this point, I'd be inclined to keep it as-is until you've decided you want to keep it for the long term. If you do decide to keep it, I suggest that you replace the PT with either a known-good original or a new aftermarket version (probably not potted) with correct voltages so you can get designed-in performance. After having given the OPT issue some thought, I strongly recommend against replacing the OPT with anything other than a known-good Peerless 16458 if yours doesn't already have that. Most any other OPT no matter how good it is will most likely require you to make adjustments to the circuit for the amp to operate properly.

My last two bits of advice are: 1. Don't get overly concerned about the degree of balance or whether the amp holds balance perfectly every time you check it. 2. I don't recall if you've done this or not but if not, replace all electrolytic power supply and cathode bypass caps and the paper coupling caps.

 

[k**rkleclaire]

Cool, Thanks. I was using the wrong setting on my multi-meter! I realised that at 4am! laying in bed. wow dumb. I did get the balance set. It's been running for 5 hours no problem. Sadly it is the 13609 OP. I'll watch for correct one on Ebay for an eventual replacement. I do think in the future I will replace the PT with your suggestion but for right now I calling this a success and sit back and listen a while. it doesn't sound quite as good as I expected but maybe it needs to burn in a little. I did replace all the caps.. I improvised for the power caps instead of the multi-caps i strung a bunch of electrolytcs togather.....unorthodox, but it seems to be working.. I used high quality caps through out. Jensens and Auricaps.. So thanks for all the help.. Next is my PAS-3, I also want to do the PAS-2 that came with the W-5m but that will be another day. if you have any advice. holler.
Kirk

 

[Steve O]

Cool, <snip> Sadly it is the 13609 OP. I'll watch for correct one on Ebay for an eventual replacement. I do think in the future I will replace the PT with your suggestion but for right now I calling this a success and sit back and listen a while. it doesn't sound quite as good as I expected but maybe it needs to burn in a little. <snip>
Kirk

Kirk:

I wouldnt worry too much about the OPT being the 309. Although more failure prone than the 458, your 309 is certainly past the infant mortality stage. Most important thing now is to be sure nothing runs away so the the OPT is stressed. Also be sure to always have a load on the output.

Regarding the sound, remember that you're running pretty low on B+ due to the replacement PT you have. At the guestimated B+ I think you're running (~400V???) the amp is probably going to be out of spec for max power and distortion. Personally, I'd be looking for a replacement PT that gets you closer to design before I'd be looking for another OPT. Just my opinion.

In the meantime, enjoy the fruits of your work.

 

[PakProtector]

You'll need a pretty good transformer to run a Williamson design. The circuit uses a good deal of feedback, but with a decent OT, it is not a problem, but with a hammond, it might be....

I think the S-265-Q won't have any problems in this situation.

hey-Hey!!!,
I don't think it'll mind either. If it'll stand duty in a Williamson, it'll do better in a Mullard circuit. Of course there's other circuit options too...

I get this one from Heyboer with custom U-L taps. They can also wind the little 16309 to repair the W5's. Given that the cost will be similar( ~$100 each ), I'd go with the U-L modified S265. Get the full spread of taps at 20, 30 and 40%, and high power handling/headroom.
cheers,
Douglas

 

[vendo81]

No they mean "bass-Bal" for bias adjustment, it's set up so that when you adjust R1 the variable pot, that you read no potential on a volt meter.

Go here, they will practically tell you how to build it.

http://www.barbwired.com/andy/w5/index.htm

I'm just now ordering the parts to make two of these. I find it costs less to build your own from the ground up, and they work and sound better

Boy... if I can build a W5M copy that sounds better for less than you can buy an original for please let me know :yes: Just make sure you do a one on one comparison and make sure they actually sound better, not on paper but in person.
I have 2 modified W5M's with the 16458 OPT's. I did the 6CG7 swap, I'm using original Genalex KT66's, added separate filament transformers to take partial load off the PT as well as several other minor mods...They take a little upkeep but they are one of the nicest sounding tube amplifiers I have heard. I own several rebuilt tube amps including a Marantz 8B, 2 Fishers, and a soon to be restored Eico and Sherwood. I recently bought Mullard output tubes for the Marantz and it sounds incredible but I say the same thing every time I listen to the W5M's. Not as pretty as the Marantz but the sound is