It looks like its only part of a kit that someone purchased and did not make much of a start on. The chassis, transformers, valve bases and and choke appear to be included, but most of the valves are missing and would have to be purchased separately. The chassis has not been assembled yet. Apparently only a bit of the tag strips has been made up so far. The buyer would have to find a means to secure the transformers to the chassis.
From the TubeLab website: "At this time I have only blank unpopulated PC boards available. I do not sell parts, kits, tubes, assembled PC boards, or complete amplifiers. I simply do not have the time or financial resources to stock, inventory, and kit all of the individual parts to offer amplifier kits."
It looks like only PCBs are available now. I would have to source all the other bits elsewhere. Still a PCB may be useful as a starting point. How do modern PCBs hold up to the heat generated by valves? I thought that tag strips were used in preference for this reason, but I see many modern designs with PCBs.
UK voltage is upposed to be 230V . It measures 245V at in my area (west London) . Voltage does actually fluctuate depending on time of day . The only aspect that is stable is the line frequency . For best practice the primary should have taps to match to the local supply . I have seen quite a few valve amps that were quite literally burning up valves several times a year and stressing capacitors . The worst was an amp by Dared , which incidentally had a 230V specified transformer . I measured 7.1V at the heater pins on the EL34 . I suspect it had a transformer rated for a 220V supply , a transformer for 230V would have been better but still over spec for heaters .
316a
George (Tubelab) sells not 'just' the PCBs but has very well documented building instructions on his site. These include the partnumbers of the components for Mouser and Digikey. Sourcing made easy
Possible transformers are discussed as well.
He has his own forum here on diyaudio.
That's interesting 316a. I would not have expected 245v. Did you measure this with a DVM or an analogue meter? I will definitely check the supply in my area.
I'm curious about the stressed capacitors though. How does this manifest itself? Heat? Distortion? I would have thought that if carefully (i.e. sufficiently generously) specified, then capacitors shouldn't get 'stressed' by a less than 10% voltage variation? Those Dared amps don't look particularly cheap either.
Assuming the valve heaters are in parallel, could the heater voltage issue be overcome by having a regulated DC supply rather than a direct AC supply? Obviously more parts and hence cost involved, but presumably not difficult to add?
mullered, I will have a look at this as well later. Thanks for the suggestion and for pointing our Sowter UK as well. I have made a note.
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Any amp that can not tolerate 10% or so in voltage variation is not designed correctly.
Valves also are very tolerant, unless (again!) some designer has been pushing them to the end of their range (i.e. not correctly)
The only thing valves do not like is too much over-voltage on heaters.
Regulate them, then no problem ( I never do).
I have not seen or heard of a valve blowing in a correctly designed amp because of this.
may be on some fringe - remote area where mains-voltage fluctuates a lot more than usual.
Unfortunately that part kit has now gone. Very disappointing but I guess someone else has contacted the seller and the sale has been withdrawn. I've been considering this project for several months now so I was getting quite excited about that but will now need to look for other options.
Incidentally, mains voltage here was was 235v on the Digital multimeter and 240v on the AVO Meter. Not sue which one is more acuratem but the measurement was taken across the primary a 110v isolation transformer which I use for my Eddystone and hence under load. Clearly is is someowhat more than the nominal 230v I should be getting.
Incidentally, mains voltage here was was 235v on the Digital multimeter and 240v on the AVO Meter. Not sue which one is more acuratem but the measurement was taken across the primary a 110v isolation transformer which I use for my Eddystone and hence under load. Clearly is is someowhat more than the nominal 230v I should be getting.
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Ken, this was my understanding as well, so I was a little surprised although interested to hear 316a's experience. To me this suggests that the amp may be designed or running too close to the component limits, or perhaps fitted with sub-standard or poor quality components in order to cut costs, or components were failing anyway. Either way it seems a point worth noting.
On another note, anyone rate Quad IIs? I hear they are fairly sought after? The obvious drawback of having separate modules is the need for additional power transformers for each module, so what's the advantage of having two separate amps rather than one integrated chassis? I have seen both a pair of refurbed units as well as one ready for restoration at around and about £100 more than the top end of my budget. I'm wondering whether the one for restoration is a worthwhile investment? Restored units seems to vary in price anywhere from £600 to £1200 for a pair with controller which kind of puzzles me?
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The Quads, I have heard good things about, though I have no experience of.
The are a sought after vintage amplifier of good reputation (that, raises the price), as you know they are mono-blocks.
Each unit has it's own power supply/regulation.
Advantages of mono-blocks are :
1- Since speaker cable is detrimental to damping factor and global feedback, having left/right amps, makes it possible to put each one close to each speaker and run a short cable, if your system is a balanced one (XLR sockets?) then it is far easier to run long balanced interconnects to each amp without much penalty in sound quality (a few meters of phono cable is just as good).
2- separate amps means, better/stiffer power supply, no cross talk of signal or induced distortion between channels.
Also each unit is smaller and lighter.
If you could pick them up reasonably and do them up, good on you!
I was under the impression, you were new and were trying to keep costs down - right?
The are a sought after vintage amplifier of good reputation (that, raises the price), as you know they are mono-blocks.
Each unit has it's own power supply/regulation.
Advantages of mono-blocks are :
1- Since speaker cable is detrimental to damping factor and global feedback, having left/right amps, makes it possible to put each one close to each speaker and run a short cable, if your system is a balanced one (XLR sockets?) then it is far easier to run long balanced interconnects to each amp without much penalty in sound quality (a few meters of phono cable is just as good).
2- separate amps means, better/stiffer power supply, no cross talk of signal or induced distortion between channels.
Also each unit is smaller and lighter.
If you could pick them up reasonably and do them up, good on you!
I was under the impression, you were new and were trying to keep costs down - right?
Thanks ken for that explanation. I can see that there are advantages to having separate power amps.
I am comfortable with the idea of refurbishing a pair of Quad IIs, but I am quite new to valve amps. I am indeed trying to keep costs down and maybe the Quads are a tad on the steep side. Replacement KT88s and other good quality replacement parts are not cheap either so a refurb could prove costly. Nevertheless I if could pick a pair plus pre-amp up within or around my budget then they might be worth considering. The pair I have seen are rather tatty though but come complete with all valves and pre-amp.
On the other hand if I could save some money and still pick up something reasonably decent then so much the better so I wanted to test the waters so to speak and ensure that I avoided any pitfalls (read as cheap tat). The HFA2 is still a prime candidate otherwise.
I am comfortable with the idea of refurbishing a pair of Quad IIs, but I am quite new to valve amps. I am indeed trying to keep costs down and maybe the Quads are a tad on the steep side. Replacement KT88s and other good quality replacement parts are not cheap either so a refurb could prove costly. Nevertheless I if could pick a pair plus pre-amp up within or around my budget then they might be worth considering. The pair I have seen are rather tatty though but come complete with all valves and pre-amp.
On the other hand if I could save some money and still pick up something reasonably decent then so much the better so I wanted to test the waters so to speak and ensure that I avoided any pitfalls (read as cheap tat). The HFA2 is still a prime candidate otherwise.
The HFA 12 amp already mentioned, if modified to manual bias, will have very similar output stage to Engineer's amp.
The input stage and tthe driver section would be different, but is very good indeed. They are triode based, with a small global feedback.
I think the Quad may be a bit too picey and from what I have now heard about the power transformers failing I'm not so keen. Any of these worth considering?
World Audio EL34 - £350
Eico ST40 - £190
Croft Series 5 - £300
Rogers Cadet III - £260
Hammond monoblock - £160 each so £320 the pair. Uses Hammond valves - can these be replaced?
Would leave me a bit of spare cash for refurb work.
World Audio EL34 - £350
Eico ST40 - £190
Croft Series 5 - £300
Rogers Cadet III - £260
Hammond monoblock - £160 each so £320 the pair. Uses Hammond valves - can these be replaced?
Would leave me a bit of spare cash for refurb work.
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Well I didn't realise that the Rogers Cadet III is actually a pre-amp, so that one is crossed off the list. Any thoughts on the others? Regarding the Hammond, any thoughts on the 7591 valve used in them? Can these still be obtained and are they suitable for general audio use? I understand they are more suited to guitar amps? Is that correct?
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7868 is pretty well the same as 7591 except different base and pins. Both are still in production by EH & JJ and now TS with a really nice new 7591.
They are well regarded for Audio and in NA all the big makers used them back in the day like Scott, Fisher, Macintosh, Eico, Sherwood etc. The Eico ST-40 used them and should be nice for a rebuild. Eico ST-70 also used them and had more power with bigger Output Transformers. They were an easy to drive tube like the smaller EL84/6BQ5 so the circuit could be simpler.
They were also used by Pioneer & Sansui, Kenwood etc. in Receivers/ Amps.
I don't think they were used much in NA for Guitar Amps as far as I know.
You must fully recap vintage equipment or you risk any or all of the transformers.
Don't just plug them in to test either without a dim bulb tester (better with a variac in series) and never run a tube amp without a load (speakers or big resistors) hooked up.
They are well regarded for Audio and in NA all the big makers used them back in the day like Scott, Fisher, Macintosh, Eico, Sherwood etc. The Eico ST-40 used them and should be nice for a rebuild. Eico ST-70 also used them and had more power with bigger Output Transformers. They were an easy to drive tube like the smaller EL84/6BQ5 so the circuit could be simpler.
They were also used by Pioneer & Sansui, Kenwood etc. in Receivers/ Amps.
I don't think they were used much in NA for Guitar Amps as far as I know.
You must fully recap vintage equipment or you risk any or all of the transformers.
Don't just plug them in to test either without a dim bulb tester (better with a variac in series) and never run a tube amp without a load (speakers or big resistors) hooked up.
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Did you manage to get the Croft?
I wanted it, but didn't bid, I hope it was you.
Ken, the seller also claimed it was noisy due to the number of valves in it. I'm not sure whether that is the cause, probably more likely to be down to failing caps or valve, but it did make me hesitant to bid. Although I tend to put function above looks, I did think it looked a bit ugly so it was not my first choice.
The World Audio EL34 amp I mentioned looks much nicer, but its clearly not original vintage as it has a much more modern look about it. The output transformers look reasonably robust but it apparently has a torroid under the chassis for the power transformer. Not seen these in valve amp before. I know they can work well for transistor amps but are they suitable for a valve amps?
The Quads went for £700 which was well above my budget. There is another pair for £590 with one faulty valve and no pre-amp, so I could end up spending a similar amount or more to get a working setup. I am therefore not pursuing this option.
Other than the World Audion, the HFA and the Eico are still on my list.
Again with the Hammonds I would have to get a pre-amp and run them off the mains in series, so due this complication they are not my first choice either.
The World Audio EL34 amp I mentioned looks much nicer, but its clearly not original vintage as it has a much more modern look about it. The output transformers look reasonably robust but it apparently has a torroid under the chassis for the power transformer. Not seen these in valve amp before. I know they can work well for transistor amps but are they suitable for a valve amps?
The Quads went for £700 which was well above my budget. There is another pair for £590 with one faulty valve and no pre-amp, so I could end up spending a similar amount or more to get a working setup. I am therefore not pursuing this option.
Other than the World Audion, the HFA and the Eico are still on my list.
Again with the Hammonds I would have to get a pre-amp and run them off the mains in series, so due this complication they are not my first choice either.
World audio is a nice amp, though I wonder where the mains transformer is? it usually sits on top between the output transformers.
The croft was a nice one, but just like HFA12 they were made to work with low output pre-amps, they can get a little noisy.
Since you will be using them with a DAC, you should bypass the first tube stage (arrange the NFB to the 2nd stage), give them a little TLC on wiring and powersupply components, and they go silent, no big'e!
My clone of HFA12 was so noisy, the guy sold it as "for parts only" - now if you put your ear right to the speaker, in a quiet room, you might hear a little hum, if you concentrate hard!
at 4 inches away, nothing!
BTW I have 20-20 hearing
(though my mum always said I don't listen)
The croft was a nice one, but just like HFA12 they were made to work with low output pre-amps, they can get a little noisy.
Since you will be using them with a DAC, you should bypass the first tube stage (arrange the NFB to the 2nd stage), give them a little TLC on wiring and powersupply components, and they go silent, no big'e!
My clone of HFA12 was so noisy, the guy sold it as "for parts only" - now if you put your ear right to the speaker, in a quiet room, you might hear a little hum, if you concentrate hard!
at 4 inches away, nothing!
BTW I have 20-20 hearing
(though my mum always said I don't listen)
The Rogers cadet III is actually an integrated stereo amplifier from the 1960's.
It is 10 watt per channel so fairly efficient speakers are required. The low end
bass is somewhat flabby. Here is a link to some info on it.....
Rogers Cadet III - Vintage - Integrated amplifiers
The Rogers cadet III is actually an integrated stereo amplifier from the 1960's.
It is 10 watt per channel so fairly efficient speakers are required. The low end
bass is somewhat flabby. Here is a link to some info on it.....
Rogers Cadet III - Vintage - Integrated amplifiers
The OPT's (Output Transformers) are really the determining factor in a tube amp's sonics in that they are very expensive to now buy really good ones, so vintage may be the best answer on your budget.
The Eico ST-40 & 70 can be a great value in that department and being integrated solves the preamp problem. They do not go for big $ do to their low $ looks. They are also easy to work on with P2P wiring and ample room under chassis for easy refurbishing /repair.
The Eico ST-40 & 70 can be a great value in that department and being integrated solves the preamp problem. They do not go for big $ do to their low $ looks. They are also easy to work on with P2P wiring and ample room under chassis for easy refurbishing /repair.
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