Heathkit W-5M Help for Noob

Pics of surgistors make me think the device along the top edge in your last pic is that. Sounds like what we'd now call a PTC thermistor. Basically its high resistance when cold, and low resistance when hot. It slowly brings voltage up instead of the usual surge of current that happens when you throw the switch. Its nice for the switch and the transformer.

eico-hf-87-hf-89-hf-89a-surgistor_1_95ec3e5b8f00c0c8dd56529338c4787b.jpg


Looks like its fairly mechanical in nature. I see what looks like a bi-metal strip along the bottom and what I presume must be contact points at the left. Taking a guess at it, initially the current runs through the resistor until the heat causes the bi-metal strip to bend over and close the connection across it.

A modern part would be something like an Amphenol CL-80. They aren't mechanical but functionally serve a similar purpose.
 
Owen, I expect you will get a variety of recommended actions to take (or request of the tech guy), and that will then lead to some level of compromises ($, and tech ability). It sounds like your keen enough to at least spend some $ on a tech, and at least show some interest in what actions should make it on to the action list.

I think we all like the actions directed at alleviating potential damage to the amp and its parts. After that then the typical focus moves to checking and tuning the audible performance. Both of these areas can get technical. Perhaps not easy to collect all that together from a few quick forum posts.

You may want to elaborate on your intended use of the amp, given it is a monoblock with 2Vrms FS input, as that could allow better suggestions (such as putting the KT66's away in cotton wool). It's even worth explaining the speaker you will use, as a poorly performing Williamson may stress tweeters or require some management of sub-woofer response. The W5M does manage higher frequency instability, but it would normally be checked, but needs to be protected from very low frequency content (<10Hz) or audible performance could degrade.
 
Two things that i don't think have been touched on here worth mentioning. IIRC these are known to have flaky power transformers. All the more reason to make tech aware and make sure it only gets tested through a DBT until its sorted out. Also these were made to to run on 117vac. Being how you more than likely have 122-123 vac coming out of your wall now you should look into a bucking transformer. Your tech can help you with this (I understand some use multiple CL-80s to drop line. I'd guess you'd have to see). I'm not so concerned with the bump in the supply voltages. I just think the filament voltages will be high shortening tube life. Something to consider.
 
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Owen, I expect you will get a variety of recommended actions to take (or request of the tech guy), and that will then lead to some level of compromises ($, and tech ability). It sounds like your keen enough to at least spend some $ on a tech, and at least show some interest in what actions should make it on to the action list.

I think we all like the actions directed at alleviating potential damage to the amp and its parts. After that then the typical focus moves to checking and tuning the audible performance. Both of these areas can get technical. Perhaps not easy to collect all that together from a few quick forum posts.

You may want to elaborate on your intended use of the amp, given it is a monoblock with 2Vrms FS input, as that could allow better suggestions (such as putting the KT66's away in cotton wool). It's even worth explaining the speaker you will use, as a poorly performing Williamson may stress tweeters or require some management of sub-woofer response. The W5M does manage higher frequency instability, but it would normally be checked, but needs to be protected from very low frequency content (<10Hz) or audible performance could degrade.

So I have a mint Electro Voice Aristocrat speaker that has been sitting in my office for six months that I want to pair with the Heathkit amp. My intention is to have a nice mono system to play jazz, classical, and ambient music at moderate volumes. (Not loud enough to scare my clients.)

I'll probably pick up a cheap CD player to hide away somewhere and use that for an input, or there is always the trusty ipod. You guys are pretty protective of the KT66's, huh? Valuable tubes!

Maybe someday if I find a nice rek-o-kut turntable I'll hook it up as an analogue system. But of course then I'd need to find the pre-amp. Luckily the matching pre is all over ebay so if I get ambitious that's possible.

My priorities are to make the amp safe to operate without risk of damage to components, and to preserve as much of its original tone as possible. My sympathies lean toward replacing only components that are failing, or at imminent risk for failure that would damage other parts of the amp. This, I understand is a surer path towards preserving the authentic flavor of the amp, though I'm open to contradiction.
 
Two things that i don't think have been touched on here worth mentioning. IIRC these are known to have flaky power transformers. Al the more reason to make tech aware and make sure it only gets tested through a DBT until its sorted out. Also these were made to to run on 117vac. Being how you more than likely have 122-123 vac coming out of your wall now you should look into a bucking transformer. Your tech can help you with this (I understand some use multiple CL-80s to drop line. I'd guess you'd have to see). I'm not so concerned with the bump in the supply voltages. I just think the filament voltages will be high shortening tube life. Something to consider.

Wow, ok. Good information but not sure that I can integrate that with my tech. I don't think he's ever worked on this amp before but I'll mention that anyway.
Also, what's a DBT?
 
Pics of surgistors make me think the device along the top edge in your last pic is that. Sounds like what we'd now call a PTC thermistor. Basically its high resistance when cold, and low resistance when hot. It slowly brings voltage up instead of the usual surge of current that happens when you throw the switch. Its nice for the switch and the transformer.

eico-hf-87-hf-89-hf-89a-surgistor_1_95ec3e5b8f00c0c8dd56529338c4787b.jpg


Looks like its fairly mechanical in nature. I see what looks like a bi-metal strip along the bottom and what I presume must be contact points at the left. Taking a guess at it, initially the current runs through the resistor until the heat causes the bi-metal strip to bend over and close the connection across it.

A modern part would be something like an Amphenol CL-80. They aren't mechanical but functionally serve a similar purpose.

Nice! That does look like what that is. I can get in there and check. Is there any merit to messing with it, i.e. replacing it?
 
If that does actually have a mechanical contact, I can see where that could get questionable. I'd probably swap it for a modern equivalent just for reliability reasons.
 
I doubt the 'Surgistor' has a strong temperature dependant resistance - rather, the resistor is sized and rated to cope with the initial current from equipment within the rated power range (100-275W), and dissipating sufficient heat to cause the bimetallic switch to close (and to stay closed). If possible, the tech needs to clean the switch contact, and confirm the device works appropriately. If the tech knows his 'contacts' he can advise how pitted/bad the contact is. I'd keep the device if it is working - although a small sheet of nomex insulation paper sandwiched between the part and the chassis may provide some peace of mind, as that part is large and has a lot of exposed metal and is close to the chassis.
 
document exactly what he does, he should do this to annotate the bill, but bring a tape recorder,
or better yet, a video camera, to record the details unless you have a great memory. then you
document all that has changed (eg R35 was xyz replaced by a Caddock film, etc)

three benefits, if and when you sell then it adds value if the changes are documented so us
guys who think we know what we're doing can't or still will complain about hack job on this
pristine, valuable, parts-matching, holy-grail (applies to cars, tubes, cartridges, guns, coins,...)
unit.

second benefit is that the next guy fixing this unit won't scratch his head when he sees a 2017 Wima
cap in a 1950's unit, LEDs replacing bulbs, bypassed signal sections/caps/etc, and then he can
ascertain whether the previous hacker undid his previous hacker. then he can really fix, blueprint,
and upgrade the unit and at a lower cost.

third and last is that you learn and perhaps even DIY and become a King of W5Ms.
 
Ok, but in summary: should I be asking my tech (who mostly works on guitar amps) to do anything besides test all the components replacing them as needed and clean tube sockets? The output tranny sounds flakey even with the surgistor. Is it necessary to drop line voltage from 120v or something like that?
Remember, I'm a noob. Just trying to get this amp up and running without destroying its tubes, opt, or character. Thanks again.
 
Ok, but in summary: should I be asking my tech (who mostly works on guitar amps) to do anything besides test all the components replacing them as needed and clean tube sockets? The output tranny sounds flakey even with the surgistor. Is it necessary to drop line voltage from 120v or something like that?
Remember, I'm a noob. Just trying to get this amp up and running without destroying its tubes, opt, or character. Thanks again.

Running it on less voltage is a good idea, but it's not something for the tech to do, it can't be done internal to the amp. It means you need to get a variac, or make a bucking transformer. Second option being a lot cheaper and more domestic friendly. If you search for bucking transformer on here it will turn up lots of discussion and plans. That's not a bad newbie DIY project :)
 
Sorry for late reply.
DBT
Dim bulb tester. Google it. It protects during start ups by not letting unit see full voltage. I'm confident your tech is well aware what it is (and for)
You can google it. Also a worthwhile beginner project.
If you hit a dead end , ask?
 
I'd probably suggest going straight for new coupling and electrolytic caps. I would not worry about testing them. Even if they work today, that thing was probably built when Eisenhower was in office and they were not "forever" components. Test the resistors to make sure they are in spec, and clean the sockets. Honestly there isn't much else in there. Tube amps are fairly low component count.

I would make sure to retain the original tubes, even if they are said to be weak until you can confirm they are in fact weak. Those KT66's are worth some coin and it wouldn't be the first time an unscrupulous person has sold a customer new tubes and "disposed" of the old ones for them. Not to cast any bad light on the guy, I don't know him from Adam. I just figure if I get the old part back, it probably is actually bad. When I worked as a marine mechanic, our policy was to put all bad parts in a box for the customer and only throw them out if we got the OK to do so.
 
Given the aim is to use the amp consistently, and to pay someone to do the servicing, then my suggested list for mid-life servicing would be:

Check the wall voltage over a few days where the amp will be put in to use - this will allow the tech to check that the heater voltage will be nominal in use.

Ask the tech to keep all removed parts for you.

Replace the 1uF 400V output stage coupling caps with 1uF 630VDC new caps.
Replace the electrolytics with the same cap value/voltage using 105C rated new parts from a reputable manufacturer.
Add two series connected 1N4007 diodes in series with each anode of V5.
Add a 4k7k 0.5-1W resistor from one end of the 300 ohm bias adjust pot to ground.

Check the value of all resistors and other caps, and replace if outside 10% tolerance, except for those parts marked * and ** which should be matched to better than 1%.

Replace the fuse with a new UL284-14 compliant fast blow 3A.
Clean the contact on the surgister, and check resistance.

Remove all valves and bring the B+ up to nominal 450VDC using a variac, and confirm no leakage through coupling caps or other stray leakage paths, and remove power and confirm electrolytic caps discharge in an acceptable time.
With valves, check the bias of the output stage using a variac to bring up the operating levels.
With nominal mains VAC, check the nominal operating voltages of all circuit points (note on a copy of page 25 voltage chart), including V2 anode voltage matching, output stage balance, and confirm V3-V4 grid leakage current is low and doesn't walk-away over 5 minutes.

With a matched resistive load on the output, check the square wave response as per page 7, and check the sinewave overload clipping level and symmetry as per page 7. Take a photo of the measured responses.

If the tech has spectrum analyser tools, then check the spectrum with shorted input and with sinewave overload signal when just below clipping, and take photos.

My recommended option would be to get a 315mA F UL 248-14 fuse inserted in the CT leg of the power transformer secondary for B+ supply.

The nominal bias power in each KT66 is 53mA cathode current and 425V Vak, so 22.6W. That's fine, but will slowly consume your already aged KT66's. The suggestion of purchasing a new matched pair of 6L6GC and getting the tech to fit them at the start can avoid time checking the KT66's and the risk of them being somewhat old and leaky and getting rejected anyway, or not lasting too long on the job before problems arise.

Operate the amp with good ventilation.
 
Congrats on a really nice amp!

The reason for fully recapping (ps & coupling caps) if you don't know is when an old cap shorts out (which it can suddenly do) you can loose any or all
the transformers and even output tubes.

Also always run a tube amp with a load of speakers or big 25W + resistors even when testing as you can have a voltage spike ruin
the output transformer (s). Tubes also don't like to be short cycled (quick off then back on). Let the tubes cool off good for maybe up to 10 minutes depending on the room temp etc.
 
xanadu, do you have any way of getting an AC mains voltage measurement where the amp will normally operate?

The amp is meant for 117VAC input, so should only be a concern if you consistently had above 125VAC imho. You may be able to loan or buy a cheap modern piggy-back plug in power meter (google lcd power meter) - that will also help you appreciate how much your electricity costs will go up with a valve amp!

There could be a lot of variation in a service technician's performance - which you wouldn't be appreciative of - so some peace of mind can be obtained by them either making up or ticking off a list of activities completed, and making up or filling out a table of measurements made, and giving you all the original parts that they replaced, and if they checked waveforms or spectra then quickly taking a photo of the result. The Heathkit manual is the reference to use to avoid any confusion: http://www.mcmlv.org/Archive/HiFi/HeathkitW5M.pdf

That sounds like an excellent vintage speaker system to use, and you may want to note the internal speakers/crossover as it looks like the parts inside could vary initially, and over the decades by others. The W5M has a loading network on its output to alleviate stability/peaking output due to differences between speakers, which is good.

A CD player or iPOD should be an excellent music source, as their signal voltage should be a few Vrms. Perhaps try and find a cd player with output volume control for headphones (hopefully that output will still have the same signal voltage). But I think you will need to buy or make a very simple stereo to mono summing interface - not sure if the iPOD could generate a mono output as an option.

I wouldn't put the amp on top of the speaker. Your source music could easily have substantial bass end content, and the amp will happily amplify whatever you can present to it, and the speaker would appear to have good low frequency response and perhaps even some added room corner enhancement, but the valves in the amp are sensitive to vibration (microphonics) and although you may not notice any adverse sound it will likely be muddying the sound a little.
 
I have a multimeter. I'll test the AC voltage soon. Great idea re: CD player with volume control. Will post pictures soon of the speaker and amp together!
 
The Aristocrat has a 12" coaxial speaker called the 12TXRB. Not quite as nice at the 12TRX but the cabinet is near mint. I mean, it's really almost perfect. The paper electro voice label on the back is perfect too. Pretty cool find for $50!
I know not to stack the amp on top of the speakers, just broke the rules for the sake of art.
 

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