Hi,
most of us might know the »Deacy« amplifier that John Deacon of Queen had built from an old radio and which is responsible for Brian May's signature guitar sound. It's main features are the germanium transistors used in any stage and it's transformer coupled output section. Even phase inversion was done with a transformer.
As there are many Ge transistors in my stashes, I have the idea to design an amplifier with these features. I think the math can easily be done for the output transformer, but I'm completely lost with the PI tranny. How do I calculate the power transistors' drive power demands and the winding ratio?
Best regards!
most of us might know the »Deacy« amplifier that John Deacon of Queen had built from an old radio and which is responsible for Brian May's signature guitar sound. It's main features are the germanium transistors used in any stage and it's transformer coupled output section. Even phase inversion was done with a transformer.
As there are many Ge transistors in my stashes, I have the idea to design an amplifier with these features. I think the math can easily be done for the output transformer, but I'm completely lost with the PI tranny. How do I calculate the power transistors' drive power demands and the winding ratio?
Best regards!
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You could measure the drive requirements for your output transistors. What matters here is large signal input impedance. The change in applied voltage divided by the change in base current gives Z. Rig up a jig to physically measure the required quantities using a dummy load resistor and your supply voltage. Static DC measurements are fine here. I get about 20 ohms for most of the ones I’ve played with, but those include some degeneration (the usual emitter resistor values). Turns ratio on the trafo would depend on what you drive it with - what kind of voltage you have available in the driver stage. You typically want it capable of somewhat more voltage swing than you need to drive your outputs to full current, because you also have to charge capacitances with it as frequency rises and that steals drive power.
Remember driver transformers were typically fed from a class A single transistor so you had important DC through primary, so driver transformer is larger than expected, must be gapped to avoid saturation, etc.
So not as easy as it looks on first sight.
Driver transformer was as large as the output one:
So not as easy as it looks on first sight.
Driver transformer was as large as the output one:
The off-the-shelf split secondary transformers available nowadays don’t like ANY DC in the primary. I tried the little Hammonds driving Ge totem poles - and even though advertised to handle 56 mA of primary current they start saturating at about 4. Couldn’t generate enough drive with only 4mA. Worked ok AC coupled off an emitter follower - but that deviated from the classic design. You probably end up winding your own. Somewhere I saw some “instructions” on winding these up starting from 10 to 20 VA EI power transformer cores.
Yes, thank you! Will have some search for and then a close look into GE's manual, as suggested.
I've also observed in old transformer coupled transistor radios that both trannys are of the same size, and I'm well aware to do the winding job by myself. Luckily, due to the low impedances I don't expect it to be as hard as winding tube OT's.
Best regards!
I've also observed in old transformer coupled transistor radios that both trannys are of the same size, and I'm well aware to do the winding job by myself. Luckily, due to the low impedances I don't expect it to be as hard as winding tube OT's.
Best regards!
There are a couple of analyses of this amp out there and the Ge contribution is minor. The basic circuit is was pretty standard (for the time) and it's a combination of cheap manufacturing & lucky accidents that made this one sound "good". Particularly a mis-matched output stage.
I'd find those before I bothered "designing" something which ends up completely unlike what you want. Here's one I just dug up. And another
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If germanium technology have nothing to do with the sound then trying a similarly mismatched amp with silicon trz should bring up similar results, but for now i doubt that as asymetrical clipping in silicon realm is Marhall's territory and i doubt Brian May wouldn't know about Marshall... I think the real germanium mistery relies in transconductance changes around the 150mv base emitter bias which don't look similar to silicon around 0.55 v. Also they look being able to naturally drive lower impedances with lower distortions as their emitter resistors need to be lower in value to provide enough feedback, basically three time lower than silicon transistor's . To my very limited knowledge about germanium trz (actually a 24 hours long experience) they can sound as clear as silicon, but here we have an amplifier that only needs to reproduce 80hz... 8 khz (electric guitar's range) as not many people would really hear 16 khz H2 and thus the transformers have quite different requirements than a hifi one being able to respond better in that range with lower inductances.A hi fi one needs tightly matched transistors and larger bandwidth transformers which puts a large pressure on transfotmer's design.They are still easier to be made than tube ones, but not realy a begginer's lunch. On the other hand its good to know that transformers were used because npn and pnp germanium transistors are quite different in specs and pnp transistors were prefered for all operations, but they used similar transistors and there was clear choice of unmatched transistors for the final pair as it was fairly easy to find identical specd transistors of the same type.So they wanted asymmetrical clipping and its associsted sound it wasn't an accident.Now...if they wanted asymmetrical clipping why didn't they choose silicon transistors for a great player...I doubt anyone would have wanted to sell unreliable amps to a well known player...
Almost any of those Japanese pocket transistor radios from the 1960ies and early 1970ies used a pair of transformer coupled PNP germanium transistors, probably 'cause it was a proven technology at the time, and even more probably 'cause it was still cheaper than a PNP-NPN complementary, which became available and usual later on.
The pages linked by thoglette say that the original Deacy was the AF section of a radio made in Southern Rhodesia. I don't think that the output transistor pair was deliberately chosen by different properties. Instead, the manufacturer either didn't care, or one transistor had been replaced in this radio's history.
Best regards!
The pages linked by thoglette say that the original Deacy was the AF section of a radio made in Southern Rhodesia. I don't think that the output transistor pair was deliberately chosen by different properties. Instead, the manufacturer either didn't care, or one transistor had been replaced in this radio's history.
Best regards!
FWIW
I had a PM-125 interstage transistor amp (2N3055 based). Sounds good on paper. Utterly gutless (and soul-less) in reality. 50W that sounded like ten and weighed as much as 100.
But the tremolo and tone controls were good.
![pm125-2pcircuit[1].jpg](https://www.diyaudio.com/community/attachments/pm125-2pcircuit-1-jpg.1015872/ "pm125-2pcircuit[1].jpg")
(From https://www.ozvalveamps.org/playmaster.html )
I had a PM-125 interstage transistor amp (2N3055 based). Sounds good on paper. Utterly gutless (and soul-less) in reality. 50W that sounded like ten and weighed as much as 100.
But the tremolo and tone controls were good.
(From https://www.ozvalveamps.org/playmaster.html )
That’s 2N3055 for you. Especially 2N3055 driving 2N3055. Not enough current gain - the Ge’s tend to be better about that. A much better implementation that I have seen is one with darlingtons (a decent driver on each 3055), being driven by the trafo and a better single ended class A stage running at a lower current.
Thank you all. Well, my primary intention isn't a Deacy amp clone, but to see if there's something with that germanium sound myth or not, i. e. if I am able to design a Ge transistor geetaar amp that sounds similar to those tube amps that I've already built or to other tube amps.
Best regards!
Best regards!
You will certainly be able to design a good sounding Guitar amp.
Even with germaniums
But it will sound/clip/compress from any Tube amp, vary different mechanisms when beyond the linear region.
All can do the "clean" thing, that´s why you could build Hi Fi amps with Germanium, Silicon, Tubes, Fets, MosFets, even weird IgBTs; the differences appear when you go into the "undocumented" areas, or beyond what the normal datasheet curves show.
Personally I´d just build one, or recycle any old radio , cassette/record player amplifier, connect itb to a GOOD speaker and drive it hard, then tweak by ear.
Then post results here
Even with germaniums
But it will sound/clip/compress from any Tube amp, vary different mechanisms when beyond the linear region.
All can do the "clean" thing, that´s why you could build Hi Fi amps with Germanium, Silicon, Tubes, Fets, MosFets, even weird IgBTs; the differences appear when you go into the "undocumented" areas, or beyond what the normal datasheet curves show.
Personally I´d just build one, or recycle any old radio , cassette/record player amplifier, connect itb to a GOOD speaker and drive it hard, then tweak by ear.
Then post results here
Yes, JMF, this certainly will be my very first step. There's already a Loewe Opta Lord 42370 portable radio here that is heavily malfunctioning, due to the tuning capacitor's zinc cancer, missing knobs, broken dial glass etc. without any hope to be revitalized. It's got an AF amp with two transformers and AC126/AC125/2xAC121 transistors.
I suspect that the culprits of the »germanium sound« aren't these transistors, at least not at first place, but the transformer pair. An OTL or complementary pair output stage might not sound that sweet in a guitar amp. Anyway, I hope that further investigations will show. As said above, there are many Ge transistors in my bins since decades, used and new ones, even about a dozen of new AD161/162 complementary pairs.
Best regards!
I suspect that the culprits of the »germanium sound« aren't these transistors, at least not at first place, but the transformer pair. An OTL or complementary pair output stage might not sound that sweet in a guitar amp. Anyway, I hope that further investigations will show. As said above, there are many Ge transistors in my bins since decades, used and new ones, even about a dozen of new AD161/162 complementary pairs.
Best regards!
I had a Phillips cassette machine that sounded dramatically better than it's competitors because it DID NOT use audio transformers. It did use germanium transistors. Small audio transformers just have too much magnetic distortion, self-resonance, and lack of enough inductance for bass. Transformers start to get good enough for music at about 50Watts. Germanium power transistors were slow and very sensitive to thermal runaway. Before MOSFETs, germanium transistors were useful as 60Hz inverters, thanks to their low saturation voltage, but otherwise, they are useless today. Slow transistors cannot be used with much feedback, so the THD is never very good. Germanium transistors were frustrating because if you ran them "hot" to improve the THD, then you ran it their thermal problems. They are the reason many people hated "solid-state" amplifiers.
No.
You said "Queen", but England, Holland, Sheba, or Stone Age was not specified.
At reply #14 JM asserts "guitar" but he's not you. At #15 you compare to guitar amps but not clearly what you are doing.
The hint that this is in "Instruments and Amps" is lost on many.
Well, not "most" of DIYaudio. Even those few who have listened to Queen may not know the geek details.
They don´t make it any clearer than this.
You-must-be-joking.
By the same parameters,somebody mentioning "F6" in Nelson Pass´ thread must very carefully state he´s talking about an amplifier (to boot, designed by him), under penalty of people discussing (and I am restricting myself to Military planes ONLY):
- Caproni Vizzola F.6, an Italian prototype fighter of 1941 (F.6M) and 1943 (F.6Z)
- F-6 Mustang, a reconnaissance variant of the North American P-51 Mustang World War II fighter
- F-6 Skyray, originally Douglas F4D Skyray, a 1950s/1960s US Navy jet fighter
- Grumman F6F Hellcat, an American World War II fighter aircraft
- Hannover F.6, civil configuration of the Hannover CL.V, a 1918 German ground attack aircraft
- Hunter F.6, a 1954 production variant of the Hawker Hunter fighter aircraft
- Shenyang F-6, an export version of the Chinese Shenyang J-6 jet fighter
- System F6, a DARPA program on developing fractionated spacecraft
- Västgöta Wing, or F 6, a former Swedish Air Force wing
I know no DIY Audio members who are not geeks.
This Forum is extremely boring to those "from outside".
So this covers the geek side.
And most who are into Instruments and Amps know "Queen" is the name of a Rock band, even if they Play Jazz, Country or Funk
Yes, presumably it´s related to Elizabeth Alexandra Mary Windsor, who else?