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Heathkit W5M rebuilds

Hi, i just finished my second W-5M rebuild. I replaced all caps and all resisters. I used 95% identical components in each, all the same caps, a little variation with the resisters..more kiwamis less rikens, assorted metals and carbon comps. My question; one amp is louder than the other! I find I need to keep the balance pot on my pre-amp at about 1:00-2:00 to keep it balanced...I have tube rolled, switched cables ext.. and concluded one amp is just louder than the other! The thing is before the rebuild this was also the case but I thought once I replaced everything they would be closer... Maybe #2 is just tired? anyone have any thoughts? all the pin readings are close to spec in both. #2 does seem to run a bit warmer to the touch and the bias pot also seems to get hot. I switched out the 12AU7's for 12BH7's and these seem to run warmer. I do have a spare 16309 op transformer that I could switch out if anyone thinks that is the issue... other than that these amps sound great!!
Thanks,
Kirk
 
Strange problem. Did you change out all the sockets? Have you ohmed out the balance pot? Are the plate voltages the same for both amps? Do the output transformers ohm out the same?
 
Hi,
Its not my pre amp I've switched that out with another unit, same thing, and I tried reversing the the cables, no luck. Today I took new readings from all the pins on every socket in both my amps. All are with in spec except the #7 pin on the 5R4GY rectifier socket I get 390 vdc and spec is 240.This is a tie point and since both amps have the same reading I 'm not worried. Should I be? I also checked the resistances on the op transformers and all seems right, I have a spare and compared the readings with that and its the same. I'm not really worried about this as I don't mind adjusting the balance on the pre amp. i just thought I'd throw this out to see if anyone else has had this experience? One final thought: The loud amp seems punchier and has more midrange..the not so loud amp seems a little duller even when i increase the volume, Again thanks, any insights are welcome.
Kirk
 
Check for oscillation on the "weak" amp... probably ultra-high-frequency stuff (30KHz and up).

I've seen parasitic oscillation (caused by anything from a bad Zobel across the output to wire dressing) cause this same symptom... wimpy power, "dull" sound and too much heat in the output bias circuit...

You will need access to an oscilloscope for this; unfortunately, there's not another good way to investigate...

Regards,
Gordon.
 
Thanks gordon,
I don't have access to an oscilliscope and my tech in the area doesn't work on heathkits!.. so unless I buy one.... that said its not really Whimpy sounding it just dosen't sound as dynamic or as loud as my other one. I'm unfamiliar with zobel's? and as I stated earlier in the post it exibited this problem even before the rebuild maybe that's the nature of the beast. The only thing that remains of the original is the PT, The OP tranny. Choke. wire and bias pot Could it possibly be a bad bias pot? or is that just the symptom not the cause?
Thanks,
Kirk
 
The Bias pot is a balance pot, meant to equalize the current between the output tubes. You can try a couple of things. It's a pain, but you can swap output transformers to see if the problem follows the transformer. You might also have a bad tube socket that is leaky. Are you using the original biasing resistors?
 
whoo.....Today the UPS guy brought me another pair of vintage Genulex kt66's so now I have a quad.....things are sounding much more closley matched.. I must say I'm not totaly impressed as prior the "loud" amp was using GE 6L6's....and I have to say the 6L6's seemed more responsive (cheaper too!) I had rolled these combinations into both amps and was convinced they sounded different in different amps, maybe not? Pariniod thinking?... I'm going to with hold judgment on the kt66's until I listen a few more days....about the hot bias control, earlier in this thread Gordon recommended tube shields on the /V1,V2 sockets.... I am using 12BH7's so I got some tall shields from the "Bay" inside the shields were coragated metal waffer things that wrapped around the tube snuggly I think this is what was making everything hot. I removed the sheet metal waffer thing and just went with the shield..seems to run cooler!...Thanks everyone for all the help.. I am slowly....slowly learning a lot of stuff and my system is getting better and better. You guys are a great help..Thanks
cheers,
Kirk
 
Surge Suppressors

Jim,

I am also doing a w5m rebuild/mod. What are you using for surge suppressors? I have some CL-60s laying around but they are good for 5a steady state. I see some CL-190s on ebay which are good for 2.5a steady state.

Also, here did you purchase your tube sockets?

Thanks!
 
Your CL-190's should be fine. I think, if I remember right, I used CL-120's, but I could be mistaken. I got the sockets of off ebay. The octals and 9 pin sockets were from ebay seller hongkongsuperseller. Be aware that there are two sizes (in outside diameter) of 9 pin chassis mount sockets. The ones that will fit the W5M's and most older amps have the smaller diameter. If you need me to send you two ebay item numbers so you can see the difference, just let me know.

Good luck!
 
Great news! To all those who have asked about the missing post pictures.....I found them! PM me if you want them.

Regards,
Jim, AB0EZ
 
Jim,

Thanks for maintaining this thread, the pictures are nice. Just beginning to update my single WFM for mono system I am planning. I am thinking of possibly updating and using the WA-2 preamp and shopping for an appropriate single speaker...

Jim Mc
 
ab0ez said:
So, the original W5M amps did not have a power switch. They were swtiched on and off via the matching preamp by bridging a connection on the AC primary side of the power transformer via the preamp power socket on the chassis. This was no longer desired. In fact, all the connections and related wiring were removed from this socket.

But where do we add a power switch without altering the chassis? Well, in addition to the preamp power socket no longer being used, the AC accessory outlets were no longer needed nor desired so they were removed. An appropriate on/off switch was added and just fit into the existing hole now vacated by one of the now defunct AC accessory outlet holes in the chassis.

A vampire RCA input jack was also added. Note that the insulating washer was used and it was verified via an ohm meter that there was no continuity from the ground side of the connector to the chassis.
Click to expand...

This last paragraph cornfuses me a tad. Was planning on getting rid of the orig RCA connectors on my 5's and see the ground side of the connector touching the mounting screws/nuts and those are in direct contact with the chassis. My VOM reads continuity to any chassis screw. I was planning on not using the insulating wafers.

Why is my situation different from yours??

Bob
 
I've got some W4s to get to this year and I consider this the tutorial to use for the level of rebuild I'd like to accomplish. Thanks for such a great chronicle.
 
suzerain said:
This last paragraph cornfuses me a tad. Was planning on getting rid of the orig RCA connectors on my 5's and see the ground side of the connector touching the mounting screws/nuts and those are in direct contact with the chassis. My VOM reads continuity to any chassis screw. I was planning on not using the insulating wafers.

Why is my situation different from yours??

Bob
Click to expand...

Bob, I don't know why my situation is different without seeing any pictures of your installation. I can only assure you that insulating washers were used on both sides of the chassis and an ohm meter check between the connector body and anywhere on the chassis showed an open.
 
Yes,
a whole hearted thanks for the detailed chronicle,
a quality rebuild indeed.

And I think a new rectifier (and perhaps output) socket - as you recommend - may help stabilize my wandering balance voltage in one of my W5. Going to try it.

Both mine W5m show continuity from outer RCA style signal input coupler to anywhere on the chassis.................. interesting.:scratch2:
 
Great amps, I have a pair of gold chassis and a pair of silver chassis. IMHO, these amps require very high quality NOS tubes to really sing.:music:
 
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