Heathkit W5M Thoughts

[8xlaxx]

Nice seeing many threads and posts about these W5M amplifiers on AK. Truly a wealth of knowledge here and of course, I'm kinda late to the game on these lil' gems.

I recently acquired two W5M amplifiers with matching WA-P2 preamps. Both W5Ms have their original KT-66 tubes and Mullards that all tested good/strong.

W5M #1: Was sitting in a dry garage for 40+ years. Has a 16309 OPT that ohm'd out at 631ohms on the output tubes of pin 3. I removed the 5R4 and connected a variac and tested the 54-32 Stancor PT and it showed no filament DC voltages on output tube pins 2 & 7 (both). Looks like a dead PT! Fuse was good. I measured 116VAC across the fuse and surgistor and to the front of the skirt socket pins 6,7,8. I had to connect one of the WA-P2s to use the On/Off switch to get these measurements. Got tone/continuity when touching pins 2 & 7 on both output sockets (powered off), again looks to be a dead PT.

W5M #2: Was purchased to get the mono-block project going even though not a matched pair. It has a 16458 OPT that ohm'd out at 481ohms on the output tubes of pin 3. That's all the testing I've done so far on this amp.

I'm wondering what might be a good decision on replacing the PT on W5M #1? or should I bag the whole idea of mono-blocks and sell amps, pre-amps for parts? I've got some sentimental attachments W5M #1 as it was my pop's amp, he was the original builder, etc. Be nice to honor his memory but I'm sure he'd be OK with me parting with it if it becomes a money pit. I could recoup the money invested so far in W5M #2, in selling off the KT-66 and Mullard valves in both amps.

Just wondering what others in this situation have considered doing and what the outcomes were? Resources on a a 'correct spec-d' PT would be interesting but then again, the Peerless 16309 OPT might get flaky one day and then I'm back to square one.


I want to thank @dcgillespie for helping me with the testing points for W5M #1. Again, many thanks!

 

[s-petersen]

I had a few w5m's, I sold them, as they weren't very reliable, and I had many other amps to choose from

 

[8xlaxx]

I had a few w5m's, I sold them, as they weren't very reliable,...

^^^Thank you for sharing the direction you took. Starting to get first hand experience in regards to the reliability issue you mentioned. A bit discouraged as I considered the project worthy. Maybe awakening the tube gurus here in efforts to find a solution, on which path to take, is reasonable? Be nice to hear from @Steve O @PakProtector @Brice on their recommendations. We'll see. Suggestions welcome.

 

[tcdriver]

Yes, the W5M do have a reputation for failing transformers. They also have a reputation as one of, if not the best sounding amplifiers of their era. Considering the sentimental value and the fact that the amplifier sounds so good, I would definitely repair it. There are individuals that rebuild transformers, which would be one way to go and the other option is to find a replacement power transformer.

I had a Heathkit W4M with a failed power transformer. I purchased a replacement and do not regret that decision.



In system:

 

[primosounds]

Nice seeing many threads and posts about these W5M amplifiers on AK. Truly a wealth of knowledge here and of course, I'm kinda late to the game on these lil' gems.

I recently acquired two W5M amplifiers with matching WA-P2 preamps. Both W5Ms have their original KT-66 tubes and Mullards that all tested good/strong.

W5M #1: Was sitting in a dry garage for 40+ years. Has a 16309 OPT that ohm'd out at 631ohms on the output tubes of pin 3. I removed the 5R4 and connected a variac and tested the 54-32 Stancor PT and it showed no filament DC voltages on output tube pins 2 & 7 (both). Looks like a dead PT! Fuse was good. I measured 116VAC across the fuse and surgistor and to the front of the skirt socket pins 6,7,8. I had to connect one of the WA-P2s to use the On/Off switch to get these measurements. Got tone/continuity when touching pins 2 & 7 on both output sockets (powered off), again looks to be a dead PT.

W5M #2: Was purchased to get the mono-block project going even though not a matched pair. It has a 16458 OPT that ohm'd out at 481ohms on the output tubes of pin 3. That's all the testing I've done so far on this amp.

I'm wondering what might be a good decision on replacing the PT on W5M #1? or should I bag the whole idea of mono-blocks and sell amps, pre-amps for parts? I've got some sentimental attachments W5M #1 as it was my pop's amp, he was the original builder, etc. Be nice to honor his memory but I'm sure he'd be OK with me parting with it if it becomes a money pit. I could recoup the money invested so far in W5M #2, in selling off the KT-66 and Mullard valves in both amps.

Just wondering what others in this situation have considered doing and what the outcomes were? Resources on a a 'correct spec-d' PT would be interesting

I agree with TC, that if you have the will rebuilding the units will give you a very nice sounding pair of amps. I have rebuilt the amp in stock form only and that sounds very good. I might have a PT from a unit with a bad OPT if you are interested. It will take me while to find it as the storage unit is more storage than organization.

 

[8xlaxx]

I agree with TC, that if you have the will rebuilding the units will give you a very nice sounding pair of amps. I have rebuilt the amp in stock form only and that sounds very good. I might have a PT from a unit with a bad OPT if you are interested. It will take me while to find it as the storage unit is more storage than organization.

@primosounds PM sent.

Also, I plan to continue this thread and update it in making decisions about moving forward. I received a nice PM from a member that recommended Hayboer. I spoke with Arlyn today. Very nice gentleman who provided me with some legit options.

 

[8xlaxx]

Yes, the W5M do have a reputation for failing transformers. They also have a reputation as one of, if not the best sounding amplifiers of their era. Considering the sentimental value and the fact that the amplifier sounds so good, I would definitely repair it. There are individuals that rebuild transformers, which would be one way to go and the other option is to find a replacement power transformer.

I had a Heathkit W4M with a failed power transformer. I purchased a replacement and do not regret that decision.

View attachment 1272731

In system:
View attachment 1272732

Nice pic and amp! After doing some research, that looks like an Edcor tranny?

 

[tcdriver]

Nice pic and amp! After doing some research, that looks like an Edcor tranny?

Yes, it is an Edcor XPWR033-120. The blue paint is something of a giveaway. The W4M uses lower B+ voltage than the W5M, so, the particular transformer I used may not be suitable as a replacement for your amplifier.

Link to my thread on replacing the power transformer on my W4M:
http://audiokarma.org/forums/index....cement-power-transformer.653694/#post-8844007

 

[triode17]

A sure way to test a power transformer for continuity is to measure the primary resistance. Providing the fuse and power switch (and any other parts in the primary path) is good, simply connect an Ohmmeter to the hot and neural prongs on the power cable and turn it on. It should measure something low like 10 or 20 Ohms. If its open, its bad.

 

[8xlaxx]

Testing pics,...
Probe to chassis, other probe to pin 2 of V4 on W5M #1:



Probe to chassis, other probe to pin 7 on V3.



3.3 and 3.4V AC,... saddening. 117V AC on variac.

 

[8xlaxx]

A sure way to test a power transformer for continuity is to measure the primary resistance. Providing the fuse and power switch (and any other parts in the primary path) is good, simply connect an Ohmmeter to the hot and neural prongs on the power cable and turn it on. It should measure something low like 10 or 20 Ohms. If its open, its bad.

If I did this, wouldn’t it toast my Fluke? Measuring voltage in resistance mode? I stand corrected if I am wrong here...

 

[triode17]

If I did this, wouldn’t it toast my Fluke? Measuring voltage in resistance mode? I stand corrected if I am wrong here...

No, no ,no, not voltage, Ohms. I should have said, pull the plug first, then measure the hot and neutral prongs. Sorry.

 

[8xlaxx]

No problem. She’s a goner,... and I’m getting tone.

 

[triode17]

View attachment 1273270 No problem. She’s a goner,... and I’m getting time.

12 ohms looks about right, that's not the problem.

 

[primosounds]

If I did this, wouldn’t it toast my Fluke? Measuring voltage in resistance mode? I stand corrected if I am wrong here...

Actually, the folks at Fluke protects us dummies, and if you had your meter on the wrong setting, it would not blow up. There are protection circuits to keep the meter from frying.
But, resistance measurement are done with the unit disconnected and for safety, the power supply caps discharged.

 

[primosounds]

Since you have no idea about the history of this amp and If you have an issue with the AC circuit, you need to start at the very beginning and check from the power cord through to each connection and finally the primary of the PT.
First, the on/off switch is made using the preamp connection or you need to make jumper at the octal socket. WITHOUT the jumper , test the 2 prongs, and the meter should show open (check to be sure there is no jumper at the accessory octal socket. If you have a reading something is wrong. with the jumper in place you should have a low resistance usually around 3 or so ohms, depending. What you are measuring is the primary circuit from the each AC leg, to the fuse, to the acc socket to black primary ac wire on the PT through the PT and into the other black wire then to the AC cord.
If that checks out the primary is good.
Next you need to check the secondary voltages. You will need a rectifier to do this test. I also suggest using a variac and SSR replacement for the 5R4. Since you already have seen damaged caps you just want to use a fairly low ac voltage so as not to jeopardize the output tranny. I believe the HK PT is something like 450-0-450 so just 20vac will give about 100vdc on the secondary. You should measure ACV on pin 4 and 6 of the rectifier socket. Hopefully, your PS circuit is still intact. You can also measure the DC voltage after the choke to see if that is ok. You can also measure the voltages on the OPT in DCV at the plate and UL connections for both power tube sockets. They should all measure close to the same. If any of the 4 voltages are off you might have a bad OPT. good luck

 

[primosounds]

View attachment 1273270 No problem. She’s a goner,... and I’m getting tone.

Actually you can test the secondary of the PT at the rectifier socket pins 4 and 6 without the tube in place. Again, best to use a variac at a low ac setting for safety. The B+ secondary should be some multiple of the primary voltage according to the specs. so, if the PT is 450-0-450 a 10% primary input should have 10% of 450 output or 45 on one leg.
Usually, i use a SSR at the same time, so i can also get DCV to test the OPT and other parts of the circuit..

 

[8xlaxx]

UPDATE:

After PMs w/ dcgillespie, I was not taking measurements correctly.

There is voltage from the PT,... lethal voltage. Be careful when measuring this.

W5M #1
Data:
6.8V AC on pins 2 & 7 V3 & 4
Pin 4 to GND.... 473 V AC rect.
Pin 6 to GND.... 473 V AC rect.
954 V AC pin 4 & 6 rect.

W5M #2
Data:
6.7VAC on pins 2 & 7 V3 & 4
Pin 4 to GND.....476VAC
Pin 6 to GND.....475VAC
Pins 2 & 8......5.38VAC
950V AC pin 4 & 6 rect.

Feeling confident to start ordering some parts at this point.

 

[8xlaxx]

W5M # 2 is stripped down at this point.

Need to find a product to get a 'lil shine out of the chassis. I'd like to keep it original but there is pitting and a few bare spots on the corners.

 

[PakProtector]

For the outputs on a W5m, I'd not bother if you're doing a new build. The easily available S265 from Heyboer is quite fine, especially at voltages and currents that would make a 16458 say 'Uncle'. The new S265 can have taps installed in any set of 10% increments you ask for( and especially in multiple sets ). Can't get that in a '458...let alone the undersize '309.
cheers,
Douglas