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Pye Hf25 restoration project

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Sonnyboy958

pfm Member
Hi there
After years of lusting over a pair of vintage valve amps and Pye Hf25’s in particular I finally tracked a pair (separately) down.

I will say from the outset I have no electrical/restoration experience and I have someone in mind to take on the project but I thought it might be of interest to the forum as I scoured the net for information about these amps.


I’ll include some photos and if anyone has some information/wisdom to impart please don’t hold back.

Thanks

Lee
 
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They look in pretty decent shape for a barn find, I bet they’ll clean up nicely. I notice some differences between them (additional components below one output transformer, giant TCC PIO smoothing cap on one etc). The first stage will be to test all the transformers (or get someone else to), it is only at that point that you can really make a call as to what needs to be done to restore them. As stated on the other thread assuming the transformers are all fine/the same I’d go for the most sympathetic restoration I possibly could to restore original function and retain maximum value. They are very rare amps and deserve to be done right (i.e. don’t fill them up with modern metal-film resistors and film caps!). I’d personally use carbon-film and Russian military PIO where available. I’ll let others recommend good restorers as it would be inappropriate for me to as forum owner really.
 
Yes, Lee,

They don't look too bad cosmetically and appear largely original albeit with some component replacement. I can only echo Tony's comments about getting the transformers and chokes checked professionally as item no. 1 on your 'to-do' list.

Can you please verify the types / makes of valves that came supplied with the amplifiers, as these are not all easily identifiable from the photos. FYI , the factory issued valves were Mullard ECC33 , ECC35, and GZ32 with a pair of GEC / MOV KT66 . If you are planning to stick to the original valve set, then these are potentially (very) expensive to replace nowadays even as good used items. Item no. 2 would therefore be getting the valves you have properly tested to see where you stand regarding future replacement options / cost.

Personally, when overhauling your amps, I would remove the non-original large block H.T. capacitor. I would also overhaul all the original top mounted cans by rebuilding them internally with 'new' components. This will ensure reliability in a 'vital' area and also maintain the cosmetic originality of the amplifiers.

Choice of the smaller, tag-board mounted capacitors and resistors depends on your personal preference as regards 'flavour' and of course, the size of your budget ! If you would like to send me a personal message including your email address, I can mail you a photo of the underside of my completely rebuilt monoblock which you can then post for reference on this thread if you wish.

David
 
They also appear to have the later circuit between the phase splitter and KT66’s: see the circuit diagram I posted in my thread for reference. From the pictures, one of your output valves looks like a 6L6 - they work but I find are not as good sonically as the KT66 and some of the earlier ones don’t much like the 450V these amps run. One amp looks largely untouched, so is ideal for reference; the other has been fiddled with, but both look great for restoration.
I like Tony’s advice but for various reasons departed from it in some ways during my restoration, especially with regard to capacitors. However I have not done anything to modify or alter any original parts so it would be easy to put mine to completely original form if required by a ‘collector’. I see no harm in trying modern fancies like film capacitors for increased reliability if the amps are going to be seriously used. One gain that modern passive components have is the decrease in ‘noise’ - I can recommend decent carbon film resistors: my amps through relatively efficient Tannoy 15” reds are now barely audible unless you put your head right up to the speakers.
I found the original wiring looms to be good quality and still entirely serviceable. The insulation material is easily heat damaged though, so care needs to be taken if you don’t want a complete re-wire. I would also check the condition of the “hum” control pots very carefully as these are not a universal feature and failure leads to confusing fault-finding peculiarities!
Feel free to pm if you’d like any more details of what actually went into mine, as I haven’t got round to posting everything.
 
As mentioned above the 6L6 is not really suitable for use in the HF25. If you decide to go down the route of fitting U.S.A. power tubes, then you will need to fit the higher rated (500v) 6L6GC type or if you're feeling flush, the high-quality 7581A variant.
 
Hi again

Thanks for all your input, it’s extremely valued and encouraging.

From what I’ve been told it’s the transformers in these amps that really sets them apart and so making sure they work and are original is something I need to make sure of. I think the rest is replaceable.

Although I haven’t got an inexhaustible budget to restore these amps I think doing it respectfully but modernising to a 21st century standard is probably the right way to go. They will be used and hopefully handed down…if anybody is interested. I would obviously like them to be safe nobody wants death by 50’s valve amp recorded on their death certificate.

I was also sent an article some time ago by a friend which stated that there are Russian tube alternatives which are both cheaper and potentially better sounding that can used with socket adaptations.

I will try and get these checked and evaluated in the next few weeks and let you know the findings.
 
Not a particularly sympathetic restoration. Will be interesting to see what a European pair make compared with recent prices for U.K. listings
 
brecklandboy said:
Not a particularly sympathetic restoration. Will be interesting to see what a European pair make compared with recent prices for U.K. listings
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They started at 3k chf a few months back, I’m tracking to see how low they go before they actually sell :) Most Swiss won’t like the vero board :D
 
It's a great shame that the chassis has been abused with lots of non-original holes drilled as part of the 'restoration process'. If they go cheap someone could perhaps carry out some remedial work to offset this vandalism but the 'improvements' made will certainly put off a lot of true vintage enthusiasts.
 
brecklandboy said:
It's a great shame that the chassis has been abused with lots of non-original holes drilled as part of the 'restoration process'. If they go cheap someone could perhaps carry out some remedial work to offset this vandalism but the 'improvements' made will certainly put off a lot of true vintage enthusiasts.
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Hi there,
Sorry to stir up an old topic, but I am desperate for some help please.
I purchased two of these after searching for many years.
I stupidly sold my first pair in 1985 and never forgave myself.

Anyway, I finally got a pair from Canada via Reverb (which had 6L6 OP tubes when I got them) and unfortunately it looks like the OP Transformers have been extensively re-wired to the point where I find the wiring unrecognisably changed. For all I know, they could be correct but as the guy has removed and changed the original tarred wires, and now even with documentation I can't be sure :(
Images of mine can be found here (reformatted web link)
hxxps://images.app.goo.gl/QBGTnXBHFk3qhf2D8

The next problem appears to be that the same guy must have seen and used grid stopper circuits from early and later HF25s.
My original pair only had one cap between the OP tubes and one resistor (per KT66) as per the later HF25s.
This pair seems to have the original design plus the later design and the result is far too many components in the grid stopper circuit.

I saw that you might be the correct person to ask and I really hope you can provide some feedback or original close up pics of the correct way the wiring should be. Especially the OPTs.
Not sure how to send a PM yet so I posted here. I hope that's ok..?
 
Hello Pablo,

If you give me a couple of days, I should be able to send you some images of the underside of one of my HF25 monoblocks. This amplifier is a later version and features the revised, factory circuit as documented above.

Although professionally overhauled it retains the original factory wiring and component layout. The output transformer sections are 'strapped' for 15 / 16 ohms.

I will send you a personal message via the conversation system requesting your email address . Hopefully, you will be able to reply. If not, please post again on this thread and we will try an alternative method of getting the information to you.
 
Having worked on a couple of old valve amps I've been on the look out for a pair of Pye mono blocks in need of some TLC. The ones I've seen so far have been a bit too pricey for barn finds or have been restored already.

Love to find an unloved pair, or a single to start with.

Some great information in this thread.
 
chiily said:
Having worked on a couple of old valve amps I've been on the look out for a pair of Pye mono blocks in need of some TLC. The ones I've seen so far have been a bit too pricey for barn finds or have been restored already.

Love to find an unloved pair, or a single to start with.

Some great information in this thread.
Click to expand...


As you may have gleaned from what information is available on the internet, the build quality of these amplifiers was a cut above most contemporaries, which was reflected in their high selling price in the mid 1950s. In some ways, they were ahead of their time. They still sound remarkably good in comparison with expensive, modern kit, despite being some 65 plus years old.
 
I have a couple of Radford amps from the 1960s, it would be interesting to compare with something like the HF25 as the Radfords were also classed as good build quality and innovative design.
 
Having spent the best part of six years tracking a pair down ( 1 in Wales 1 in Loughborough) and a further 18 months getting them recommissioned , I can only say you will not be disappointed. These are truly stunning amps.

What’s amazing is how modern they sound. And sympathetic to all music. All the warmth but none of gloopiness associated with a classic valve sound. The topology was certainly ahead of its time. Paired with a a great pair of speakers these sing.

Worth getting a decent resto done of these cos they’re an heirloom item (if the young’uns are interested).

Best of luck with the search…👍
 
Sonnyboy958 said:
What’s amazing is how modern they sound. And sympathetic to all music. All the warmth but none of gloopiness associated with a classic valve sound. The topology was certainly ahead of its time. Paired with a a great pair of speakers these sing.
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I suspect the ‘gloopiness’ is a myth, or based on amps struggling to drive entirely inappropriate modern speakers. I’ve never heard the Pye kit, but nothing slow or stodgy about Leak, Radford, Quad IME assuming a good speaker match. Just great sounding amps that just let the music out. It astonishes me how little progress has been made in 70 years. Amplifier technology was mature in the 1950s!
 
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