transformer housings are made of stainless steel cups for tea production in India
то mhouston
the circuit is very simple. 6S15P Russian driver transformer 1:1,2
300B transformer. anode voltage is stabilized. fixed bias.
Thanks so much!
A lot of good stuff here on this thread, and like many others I find SS amps fatiguing and otherwise not very compelling. Guess I drank heavily of the tube/valve Kool-Aid..
A gift from the past
Decca stereo radiogram srg500 manufactured about 1956.
Original mullard valves seem ok. I decided to make a primarily headphone line source amp for rock and roll valve sound.
I cleared the chassis of all radio components and connections.
I had some cutoffs from stainless steel oven hood extractor ducting.
It was very thin and cut with tin snips then glued with superglue. Inside I put polythene insulation.
This made nice safety covers for all the transformers and choke.
The choke was made from an old E frame mains transformer by splitting the laminations and removing the "I" pieces, then reclamping
as open "E"'s.
The audio design is ECC83 triode stage to EL84 single ended output. I hope the transformers are good quality, they are certainly heavy.
As sold the chassis was not earthed.
I got the circuit from vintage radio on the internet.
I converted the amp power input to a fused euro power socket, with earth connection to the chassis.
Input panel RCA and loudspeaker and power socket connections were to the rear of the unit.
The mains transformer had a bolt stub very handy for clipping the power and speaker cables to the chassis (see pic).
I discovered one toasty EC83 anode load which was replaced (the other channel value was 50% higher than spec probably due to age)
A preliminary switchon showed horrendous hum. (at switchoff, hum fades before amplification does).
I replaced both with 100k.
I noted the original circuit used single wire parallel ac heater supply, with chassis return. This partly accounts for the hum that was acceptable
at that time.
I decided to retain that topology, but use a well smoothed dc. I also added a separate toroidal mains transformer for the heaters.
This not only took the magnetic stress off the HT transformer, but also allows the heaters to warm up before HT is applied.
I suspect the rectifier valve and/or smoothing electrolytics (possibly the EL84 cathode bypass electrolytics too)
I replaced the caps C35,C41,C49 all 32uF 360v (in can). and the bypass C48 25uF 25v.
the first three were replaced by separate radial electrolytics 220uF, 385v.
HT
The original design used single HT supply for both channels (pretty well universal then). It has supply voltages shared at several points, including
a shared grid bias resistor. Since this was to be a headphone amp, I decided to retain this, as a certain amount of channel blending is headphone friendly.
I replaced the EZ81 rectifier valve with a silicon bridge rectifier (600v. piv, 10amp)
Output volts too high to adjust, so I used two diode 1N4007 in full wave in the equivalent to the valve rectifier and CRCLCR C smoothing.
Placed the choke in the smoothing circuit (stage2)
The final R was a mains 40W tungsten filament bulb (about1.4k). This has a nice retro feel and was mounted on the chassis top on vero board.
Decca stereo radiogram srg500 manufactured about 1956.
Original mullard valves seem ok. I decided to make a primarily headphone line source amp for rock and roll valve sound.
I cleared the chassis of all radio components and connections.
I had some cutoffs from stainless steel oven hood extractor ducting.
It was very thin and cut with tin snips then glued with superglue. Inside I put polythene insulation.
This made nice safety covers for all the transformers and choke.
The choke was made from an old E frame mains transformer by splitting the laminations and removing the "I" pieces, then reclamping
as open "E"'s.
The audio design is ECC83 triode stage to EL84 single ended output. I hope the transformers are good quality, they are certainly heavy.
As sold the chassis was not earthed.
I got the circuit from vintage radio on the internet.
I converted the amp power input to a fused euro power socket, with earth connection to the chassis.
Input panel RCA and loudspeaker and power socket connections were to the rear of the unit.
The mains transformer had a bolt stub very handy for clipping the power and speaker cables to the chassis (see pic).
I discovered one toasty EC83 anode load which was replaced (the other channel value was 50% higher than spec probably due to age)
A preliminary switchon showed horrendous hum. (at switchoff, hum fades before amplification does).
I replaced both with 100k.
I noted the original circuit used single wire parallel ac heater supply, with chassis return. This partly accounts for the hum that was acceptable
at that time.
I decided to retain that topology, but use a well smoothed dc. I also added a separate toroidal mains transformer for the heaters.
This not only took the magnetic stress off the HT transformer, but also allows the heaters to warm up before HT is applied.
I suspect the rectifier valve and/or smoothing electrolytics (possibly the EL84 cathode bypass electrolytics too)
I replaced the caps C35,C41,C49 all 32uF 360v (in can). and the bypass C48 25uF 25v.
the first three were replaced by separate radial electrolytics 220uF, 385v.
HT
The original design used single HT supply for both channels (pretty well universal then). It has supply voltages shared at several points, including
a shared grid bias resistor. Since this was to be a headphone amp, I decided to retain this, as a certain amount of channel blending is headphone friendly.
I replaced the EZ81 rectifier valve with a silicon bridge rectifier (600v. piv, 10amp)
Output volts too high to adjust, so I used two diode 1N4007 in full wave in the equivalent to the valve rectifier and CRCLCR C smoothing.
Placed the choke in the smoothing circuit (stage2)
The final R was a mains 40W tungsten filament bulb (about1.4k). This has a nice retro feel and was mounted on the chassis top on vero board.
Attachments
Hi friend, where you got the tranie's cans? Nice aspect at all. How it sound?
BEST REGARDS
the amplifier in the audio path no resistor or capacitor. sound will only wins. the sound is very accurate, fast, does not distorted. covers bought at the store utensils
What a great thread!
I'm listening to this KT-88 beastie I built a few years ago. Since the picture was taken, I've changed the output tubes to Gold Lion. Not so fond of JJ octals but love their miniatures, esp the 12AX7LPS.
The hybrid splitter works really well. U/L, 20dB feedback. Noise is less than -80 dBV, THD less than 0.1%.
I listen about 4 hrs/day.
I'm listening to this KT-88 beastie I built a few years ago. Since the picture was taken, I've changed the output tubes to Gold Lion. Not so fond of JJ octals but love their miniatures, esp the 12AX7LPS.
The hybrid splitter works really well. U/L, 20dB feedback. Noise is less than -80 dBV, THD less than 0.1%.
I listen about 4 hrs/day.
Attachments
I like that. A nice build. I also like the use of the regulator tubes. Thanks for including the schematics. You just got me thinking about my next but one build....
Thanks!
I'm very pleased with the sound of this design- which I believe is largely due to (1) the hybrid splitter, (2) the choke in the power supply and (3) regulating the supply to the first stage.
If I had it to do over again, I'd be tempted to build it as monoblocks since it's pretty heavy with all that iron -and also the power xfmr is getting large enough to make a little noise - not from loose construction, but simply from the magnetic domains in the iron re-aligning with every half-cycle. In any event, the pwr xfmr is about as big as I'd want to use in a listening environment. A toroid might do better...?
I really like the hybrid splitters- if you've never built one of these, I encourage you to try one!
If you want more pictures or design notes, I'll gladly share.
I'm very pleased with the sound of this design- which I believe is largely due to (1) the hybrid splitter, (2) the choke in the power supply and (3) regulating the supply to the first stage.
If I had it to do over again, I'd be tempted to build it as monoblocks since it's pretty heavy with all that iron -and also the power xfmr is getting large enough to make a little noise - not from loose construction, but simply from the magnetic domains in the iron re-aligning with every half-cycle. In any event, the pwr xfmr is about as big as I'd want to use in a listening environment. A toroid might do better...?
I really like the hybrid splitters- if you've never built one of these, I encourage you to try one!
If you want more pictures or design notes, I'll gladly share.
Thanks for the offer. To be honest, I am happy to build just from the schematics that you've drawn. Very clear.
Regarding the power supply - yes, a toroid might help, but it's not a guaranteed solution. The other way to re-arrange things is to keep a single transformer but to split everything after that for the two channels. So you end up with separate rectifiers, reservoir capacitors, chokes, etc. My everyday amp is a bit like that but without the chokes - http://www.diyaudio.com/forums/tubes-valves/234537-what-your-every-day-amp-3.html#post3463034
The hybrid splitter and balanced driver look interesting. Worth studying further.
I agree with diodes. The 81 further is not an audio valve probably better to control it. About 82 Different animal. To Popilin friend is a nice tube. SN7 is better- Did you tried 5751? ECC808?
Best Regards for you.
I have a pair of Heathkit EA-3 p-p 6BQ5 amps that I have modified a bit and they sound outstanding. Problem was finding EZ81 (not so EZ). I dislike that tube because not much is as short that might sub for it, even if one switches to an octal socket. No 5 volt rectifier filament winding here so a 5Y3 IMO ideal, isn't a sub even with a socket swap.
The cabinet is so low on that amp that you have to select short 6BQ5's or the tips will stick out through the air vents in the cabinet top.
To be consistent with the 6.3 volt heater, I would have put a 6X5 octal in the place of the 'not so' EZ81.
Rob
Thanx for that intel. I have just naturally adopted not mail ordering anything from the US because we Canadians generally get the wind kicked out of us whenever we do by the bullsh*t charges that so called 'Free Trade" has introduced on goods crossing our border! I honestly expected ended up paying $75.00 shipping, handling, import duty and brokerage charges (that's actually what they charge you to make sure your stuff got broke), on $22.00 worth of tubes.
I'd spend a day shoe horning a 5U4 and two days custom winding two separate filament xfmers, one for each amp before I'd bend over for those bastards again like that! They got me once on a Parts Express speaker order. Two boxes of tweeters for Ten bucks a box, free shipping to Buffalo, NY, a US city immediately south and on the Ontario border with me. Landed at my door with a $180.00 shipping, handling, import duty and brokerage charges bill. At least the brokerage I was invoiced for didn't happen!
If I sound pissed and case hardened, I am!
Rob
Hi, recently I got a pair of Bogen DB130 mono amps with two 5Y3 each. I have another DB stereo with Two 6AC7 or EZ81, I tried with many solutions for replace them and the philosophy IMHO is: Take a Valve rectifier is a high cost if you encourage a new design but if you have them there, Is a better noise machine than SS diodes. You have all the windings for the heathers the only invest is get a new valve.
In this case I replace two 5Y3 for one 5AR4 and in the EZ81 i got by ebay a couple of them. Indirectly heather system is a bonus for the natural time retard that the +B arrive to our tubes. On the past I got many valves from Antique E S and they are reliable people.
Enjoy the amp!
I am certainly interested in more details on this lovely amplifier, maybe ill try out hybrid splitter in my next amp