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Restoration Project: Heathkit W-5M Monoblocks

Based on the Williamson's PP circuitory

2x 5881/6L6GCs, 2x 12AU7s, and 1x 5R4

30 watt per block

Originally handwired in 1950's

Completed on 5/18/09

I love vintage tube amps. They usually have a nice set of irons that puts many of current production irons to shame. The people back then really knew how to wind irons, partly because there was such a huge market for it and much R&D had been put into bringing hi-fi audio to the consumer market. Altec was such a company. They made some fine irons. This is one of the reasons why I been looking for a pair of W-5Ms to restore. These have two versions of Peerless OPTs - 16309 and 16458. The latter is slightly bigger and supposedly have remedied occassional failures in the 16309 (one anode and a U-L tap went open). Well, mine are equipped with the 16309 and have worked fine for last 50+ years, so I don't see such a failure forthcoming.

My plan is to keep the circuit as it is. The reason why these amps sound so good is the topology they are based on, which is the Williamson's. There is no reason to change it. Follow the pictures below for details of the restoration:



Twins separated at birth, finally reunited!


Cleaned up a little bit - the chasses were shined with Blue Magic Metal polish followed by several layers of car paint wax. These monos have different output tubes. I really like the GE 5881s in the one of the amps, so I will try to find another match pair for the other one.


These were honestly dark grey before I polished them. Under these shields are original Mullards.Cool


This is where magic happens!


This one apparently has been worked on as evdient from the recapping job. These cheap lytics will have to go. I got some nice orginal Sprague Atoms to replace them. I also have a stock HUGE Russian PIO caps that will be invested in these amps. All resistors will be checked, especially the cathode resistors. The NFB resistors (need to be at least 1% tolerance) and their bypass caps will have to replaced no matter what. I would like to keep these vintage CC caps if possible. I like their tonal quality in spite of their tedency to drft with age.


Another one to work on. This one seems all original. I also have some NOS Chatham 5R4WGAs to replace the RCA 5R4s.


After Restoration



Retubed with NOS Chatham brand 5R4WGB and matched quad of TAD (Tube Amp Doctor) 6L6GCs.



Check out those big Russian military PIO caps. They are absolutely magical. All the caps were replaced with Sprague Atoms. The best 'lytics money can buy today.



Close up pictures of those Sprague Atoms - they are a lot bigger than conventional electrolytics of the same capacitance.



Besides recapping, the NFB resistors were replaced by 1% tolerance precision resistors. The bypass caps were also replaced with mica caps.
I spent some time listening to these amps before I started restoring them to make sure that I could notice the difference, if there were going to be any. I most certainly could. The most obvious difference was that the muddiness which existed possibly due to some dried up caps was completely gone. These amps sound very much like my SET amps - prounced highs and mids with balanced bass. Those PIO caps really make the amps sound natural and less mechanical. I am most impressed with the Williamson topology and parts selection found in these vintage amps. Gotta love the robust power supply and amazing Peerless OPTs. These two seem to be the major contributor to the famous W-5M tone.

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