| exurbia |
Help please,
I have inherited 3 large cinema amps, they use 4x kt66 per channel.
If any one can help me identify the output trafos it will help me a lot. The trafos are made by ferguson and have the number OP527 on them. What i need is the connection diagram for the taps. At the moment they are set for 100volt output.
The amps were made by National in 1970, possibly in Sydney.
Photos to follow. |
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| exurbia |
| photos of amps as i picked them up. All of the kt 66's had been smashed. |
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| audiousername |
All I could dig up was this data on Ferguson Transformers' "medium fidelity" range, which clearly isn't what these cinema amps have.
http://www.retrovox.com.au/ferguson.pdf
A shame about the KT66s... The sight of those smashed valves breaks my heart :sad:
You could probably determine most of the leadouts of the transformers by having a look at how they're hooked up in the amp right now. The impedance ratio can be determined from the square of the turns raio - which can be found by applying a known AC voltage to the primary, and measuring the resultant voltage on the secondary (or vice versa). |
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| Tekko |
| Try a search for the amps brand and model number if you havent already tried that. Take a pic of the underside of the amps too. |
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| exurbia |
| For what its worth (****** all) the kt66's were brand new as the owner had just had the amps serviced, before closing the cinema. I managed to find four brand new ones in boxes that had not been smashed. These are now for sale as i have no use for them. |
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| audiousername |
| quote: | Originally posted by exurbia
the owner had just had the amps serviced |
Oh. So then they should probably be working once they get new valves, yeah?
| quote: | Originally posted by exurbia
I managed to find four brand new ones in boxes that had not been smashed. These are now for sale as i have no use for them. |
Not going to use them in one of the cinema amps?
btw, how much? |
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| exurbia |
| The kt's are of no use to me as finding another eight is too hard. My son wants to re valve using either 6l6 or 807 as they are easy to source. According to my Rider master handbook the 6l6 will sub with no adjustments. Is this correct ? I want to have a listen before i sell the amps or swap them. Personally i find the size and weight of these amps to be inconvenient. They weigh about 40 kilos each. A friend up here has suggested using two 4-125a's in pp per amp rather than a quad of kt66 etc. The power trafos are really big and have 2 secondarys one of 600 0 600, 260 0 260 a 50v bias tap and a very big 6.3 volt supply at least 12 amps according to what was being run, including the pre amp supply. Unfortunately the cabinet was damaged beyond repair, although i'm sure my other half wouldn't have let me keep it. Each amp has a balancing trafo for input and the pre is also balanced. |
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| bear |
| quote: | Originally posted by exurbia
The kt's are of no use to me as finding another eight is too hard. My son wants to re valve using either 6l6 or 807 as they are easy to source. According to my Rider master handbook the 6l6 will sub with no adjustments. Is this correct ? I want to have a listen before i sell the amps or swap them. Personally i find the size and weight of these amps to be inconvenient. They weigh about 40 kilos each. A friend up here has suggested using two 4-125a's in pp per amp rather than a quad of kt66 etc. The power trafos are really big and have 2 secondarys one of 600 0 600, 260 0 260 a 50v bias tap and a very big 6.3 volt supply at least 12 amps according to what was being run, including the pre amp supply. Unfortunately the cabinet was damaged beyond repair, although i'm sure my other half wouldn't have let me keep it. Each amp has a balancing trafo for input and the pre is also balanced. |
4-125s?
way = no.
The 4-125s require a much higher plate voltage and higher plate Z.
Also, the output tranny's configuration needs to be determined. Separate primaries per pair of tubes? Paralled tubes? Big diff in primary Z.
The 807s only make sense if there is excess plate voltage available/present. They also need a different socket and plate caps added.
Consider, depending on ouput tranny config & Z, plate voltage any of the present day tubes; 6CA7/EL34, 6L6GC, 6550, KT88 etc...
Rewiring a tube socket isn't a big deal.
Depending on the rest of the amps performance, consider strapping the tubes for triode operation. Generally speaking strapped for triode sounds "smoother" than the same amp run in pentode or UL... you lose a little power, but with 4 tubes you may not need an extra dB.
Certainly determine if it is a fixed screen bias or UL style set up for the output tubes.
You'll want to take a look at the performance of the output tranny. Probably it is a good idea to remove or reduce the effect of the cap that is doubtless across the feedback resistor. The cap is generally there to pull up the HF response. It usually causes HF ringing, visible on a square wave. Imho, it tends to sound nasty compared to the same amp without that ringing.
Back in the day, mfrs wanted to boast "20-20kHz" response so it was common to use the feedback loop to compensate for less than stellar HF response from the output iron. If ur amp is flat out to ~10kHz. or higher, you can usually do just fine by eliminating the cap. At least take the time to remove the cap from the circuit and see what the amp's response looks like without it...
If the amp is xfmr coupled to the ouput stage, its potential might be seen as greater than if RC coupled.
My thought is that if the HF response without the cap is poor and the LF response isn't particularly great either (not enough inductance in the the output iron) then fix it up and move on... If you need a decent tube bass/midbass amp and the LF is good, then it might be work keeping around for that...
_-_-bear :Pawprint: |
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| Fuling |
| Some people claim that KT66 is electrically equivalent to EL509. |
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| Tekko |
| Isen´t KT66 the same as 6L6GC ? |
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| anatech |
KT66 is pretty much equal to a good 6L6GC. Sovteks and many others won't cut it. Electroharmonix will cut it. If you can find 7581A's you will have a great sub. In North America these are frequently branded as 7581A/KT66. I've used these and they are wonderful. Try good 6L6GC's first.
Bear, heater current. 6CA7 and EL34 draw a fair bit more that KT66. At least in my manuals they do. The difference X 4 is a bit much.
-Chris |
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| astouffer |
Those transformer cans look more like Peerless than anything.
Adam |
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| bear |
| quote: | Originally posted by anatech
KT66 is pretty much equal to a good 6L6GC. Sovteks and many others won't cut it. Electroharmonix will cut it. If you can find 7581A's you will have a great sub. In North America these are frequently branded as 7581A/KT66. I've used these and they are wonderful. Try good 6L6GC's first.
Bear, heater current. 6CA7 and EL34 draw a fair bit more that KT66. At least in my manuals they do. The difference X 4 is a bit much.
-Chris |
Ah yess the heaters... well ya gotta look at what the transformers say they can handle... if need be it might be possible to run a small second heater xfmr under the chassis or on top to run one of the pairs... being indirectly heated, it is very unlikely to cause any issues.
_-_-bear :Pawprint: |
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| mobyd |
Those smashed KT66s make me feel rather ill !
Luckily I found my cinema amps before the vandals had a crack at them.
Also uses pp parallel KT's |
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| SHiFTY |
Why not just re-tube with KT66? You can buy cheap russian and chinese ones that are supposed to be very good indeed, and they are not much more expensive. If the amplifier is well designed they won't be too stressed and should last a long time.
KT66 is the hi-fi version of a 6L6GC, made with different grid and anode spacing specifically for audio.
You should be able to simply plug and play with any of the 6L6GC variants out there, without any change in the circuit and it will still work fine.807s are the same as well, but you will need to change sockets and also check the dissipation isn't excessive.
However KT66 look much cooler...
:edit: whoa! Crazy big cinema amp / room heater you got there! Where's that from then? |
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| EC8010 |
Those amplifiers look well worth reviving. The size of the transformers compared to the valves suggests that they are of decent quality (oh, and the weight you complained about is also a good sign). The question is more whether the driver department is up to the job. As for getting eight more KT66, NOS GEC KT66 are available, they're just rather pricy (typically £70 each). Of course, you might feel that you don't need all three amplifiers to be working at any one time, in which case you only need four more KT66.
A photograph of the insides would be very useful, as would any indications as to what the other valves are/were. |
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| exurbia |
as requested, The other valves that survived were 2 or 4 6sj7.
I'm not positive about this as only two whole ones were in sockets. the other sockets only had bits in them :bawling:
here are a few more photos. |
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| exurbia |
Many thanks to everyone who has replied to my query about these amps.
The beer midget (my lovely other half) has said either they go or she does. I told her how much i'd miss her and that i respected her decision.
What to do ??:confused: |
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| audiousername |
| quote: | Originally posted by exurbia
The beer midget (my lovely other half) has said either they go or she does. I told her how much i'd miss her and that i respected her decision. |
:D
| quote: | Originally posted by exurbia
What to do ??:confused: |
Send this way for safe disposal! (the amps, not the wife ;) )
But seriously, they look like they may really be worth saving. The big, heavy transformers alone indicate that they may well have been high quality amps in their day. Can nothing be done to dress them up to increase the spousal acceptance factor? |
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| exurbia |
| the one i forgot. |
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| exurbia |
Spousal acceptance is not too difficult, she already lives with speaker baffles that are floor hungry. The amps may be worth saving but rejuvenating them is too time consuming for me. My original plan went something like this.
1 Find someone willing to do a rebuild/repair
2 Pay them for their services
3 Pay them either with money or kind ( i have a vast collection of valves etc,etc.
As we live in the nor west, freight cost would kill the transport of the whole lot.
Plan 2 is
1 find someone who can test and configure the output trafos then i could cajole my son into doing the rebuilds. |
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| EC8010 |
| That last photograph shows that the amplifiers were built quite nicely. They definitely need to be refurbished. I have eight NOS GEC KT66. |
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| audiousername |
It may be possible for you to determine the connections of the output transformer yourself.
Looking at the last picture you posted, pin 4 (the screen grid) on all valves is connected to the solder tag in the middle - this suggests they're configured in fixed screen mode, rather than ultralinear. The yellow wire on the left sockets, and the blue wire on the right sockets are the anodes of the valves, and these would be going to each end of the primary winding of the output transformer. The connection between the output transformer and the power supply will be the centre tap of the primary.
Determining the secondary connections won't be quite so easy. Sections of the transformer which measure <1W DCR with a multimeter are likely to be secondary connections. Applying a known AC voltage across the primary and measuring the resultant voltage across the secondary will allow measurement of the turns ratio, and the derivation of the impedance ratio as the square of the turns ratio.
Sorry I can't be more helpful, it's a little hard trying to explain these things in words. |
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| audiousername |
| Oh, if you're just going to restore them like EC is suggesting, it shouldn't be necessary to get all the specifications for the OPTs since they should have been designed for that service. |
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| exurbia |
Thanks everyone :)
Restoring these t the original condition is not what i had in mind.
Plan 3
1 use the amps but set up for class a operation
2 put the chassis into a nice frame/plinth
3 listen
4 become a convert to valve power amps
5 stick with my HE setup
At the moment i use a valve pre with big big solid state amps the whole set up is active using a behringer ultradrive pro and 2496 ultracurve. The system has plenty of headroom as it uses pro audio drivers . |
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| audiousername |
:(
It would have been nice to see them restored. Oh well.
Trying to describe how to redesign these amps is probably a bit much to try and explain on a forum. I could try, but I don't think I'd be very successful...
The ideal situation is where you'd be able to do it yourself after reading a book or two, but that's going to take up quite a bit of whatever spare time you have...
Hmm... |
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| exurbia |
Jason, thanks for your time and smarts. The guy i got these from tells me they were set up for class B. They wanted as much power as possible for the field arrays.
After reading through many of the posts in 'tubes' i had come to the conclusion that class A was the way to go with them. Any suggestions are welcome but doing the rebuilds is beyond my ken. I can follow instructions and swap components. My field is high power locomotive and marine engines, i build speakers for a hobby and usually buy my electronics ready built. The exception is building other peoples designs, like i said i am good at following directions and doing a bit of design. |
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| anatech |
Hi exurbia,
Too bad you can't hide 'em. I'd rebuild them and listen (start with one). You can increase the plate current to normal levels for the plate voltage and listen again. If you like, fix the rest and mount out of sight. I think that is the biggest problem with the WAF. I got me one too and we co-exist. Good thing she really likes music!
-Chris |
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| audiousername |
If the amps are running in class B, the HT voltage will probably be quite high, and the idle current quite low (to remain within anode dissipation ratings). If you're wanting to modify them into class A, you will have to significantly increase the idle current. Thus, to remain within ratings, one would have to either change to valves with a higher anode dissipation rating, or lower the HT voltage. Having a quick look ot one of the pictures you posted, it seems the power transformer has multiple taps, so the latter option is likely more viable since it won't introduce as much additonal heat into the space on the chassis between the OPT and power tx.
However, instead of going the PPP pentode route, since the KT66 can handle quite a few volts on the screen, have you considered PPP triode connection? |
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| exurbia |
Jason,
I would consider anything, even putting my DA42 triodes in if that were possible.
The beer midget understands the need for amps, she just has problems with the quantity that we have.
I would really like to see these running again and to hear them. Beer midget has suggested selling one with the remaining KT66 quad, and using the funds to pay for the restoration of the others. |
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| anatech |
That may be a plan. Current KT66's are good.
Don't get hung up on class A. There are other issues with that. Listen to them first and then change to some level of class AB.
-Chris |
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| Ed Sawyer |
IMNSHO, these are clearly high-quality amps. The construction level speaks to that, definitely cut of the cloth ala Western Electric and the like. They didn't do anal wire lacing like that on cheap crappy amps. also, the size of the iron speaks to the quality. and KT66s were not something commonly specc'ed.
amps like these deserve to be restored before doing anything else with them. If you need/want to hack on something and get your feet wet, find something else or buy a bottlehead kit or something. Don't trash a great set of amps like these. nothing you could do them from a diy/hacker standpoint would improve their value or likely even their sound. |
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