Hi,
I've just build a 1 watt Mullard amplifier from the Mullard book "Transistor Audio and Radio circuits" (1st Ed.) but replacing the germanium AC128 and AC127 transistors to silicon transistors TIP32 and TIP31.
The sound is ok, but can anyone suggest any modifications to optimize the use of the silicon transistors?
All the best.
I've just build a 1 watt Mullard amplifier from the Mullard book "Transistor Audio and Radio circuits" (1st Ed.) but replacing the germanium AC128 and AC127 transistors to silicon transistors TIP32 and TIP31.
The sound is ok, but can anyone suggest any modifications to optimize the use of the silicon transistors?
All the best.
You should replace the interbase resistors by two 1N400x diodes.
Anyway, the circuit is not very safe without emitter resistors, it could very easily go into thermal runaway.
Anyway, the circuit is not very safe without emitter resistors, it could very easily go into thermal runaway.
Actually on the first edition there is a 10W amp on page 39 (with AD162 ans AD162 also Germanium) and another 10W hi-fi amp on page 102 (fig. 71) with BD131 and BD132 which are Silicon.
The 1 Watt amp works in common-emitter configuration and the 10W that you refer is in common-collector configuration. Does the emitter resistors prevent the thermal runaway in both configurations?
I don't see how to adapt the circuit of the 1W amp, making it similar to the 10W, without changing all the circuit . This 1W amp has a relatively low part number, and that's the primary reason that led me into building it.
Cheers.
The 1 Watt amp works in common-emitter configuration and the 10W that you refer is in common-collector configuration. Does the emitter resistors prevent the thermal runaway in both configurations?
I don't see how to adapt the circuit of the 1W amp, making it similar to the 10W, without changing all the circuit . This 1W amp has a relatively low part number, and that's the primary reason that led me into building it.
Cheers.
Why are you wasting your energy and money on a design that is 40+ years old. Better designs with similar or smaller parts count and superior performance are abound. E
Hi TCA.
My Mullard book is the second edition so the page and fig numbers have shifted a bit, but the circuits discussed seem to be the same ones. The 1W amp using AC127/128 is clearly in common collector, the emitters are tied together and drive the speaker via capacitor C6.
The 'Deacy' amp you refer to is interesting. The name 'Deacy' is almost a certainly a simple corruption of D.C. as it's run off a battery, so as to distinguish it from the VOX AC30.
All I know 9of the circuit is what is implied from the text of the description.
It is a germanium design and uses one or two transformers.
There were a few similar circuits floating about in the early days of germanium which sort of mimiced valve designs. Some had a driver transformer and output transformer and some had just the driver with the output directly coupled usually via a capacitor.
The tonal (overdrive) characteristics derived from the use of the transformer(s) and germanuim transistors.
Replacing the germanium with silicon in a transformerless design is unlikely to give you the distortion characteristics you may be seeking, but thats no reasong to stop experimenting, keep going!
Regards
Henry
My Mullard book is the second edition so the page and fig numbers have shifted a bit, but the circuits discussed seem to be the same ones. The 1W amp using AC127/128 is clearly in common collector, the emitters are tied together and drive the speaker via capacitor C6.
The 'Deacy' amp you refer to is interesting. The name 'Deacy' is almost a certainly a simple corruption of D.C. as it's run off a battery, so as to distinguish it from the VOX AC30.
All I know 9of the circuit is what is implied from the text of the description.
It is a germanium design and uses one or two transformers.
There were a few similar circuits floating about in the early days of germanium which sort of mimiced valve designs. Some had a driver transformer and output transformer and some had just the driver with the output directly coupled usually via a capacitor.
The tonal (overdrive) characteristics derived from the use of the transformer(s) and germanuim transistors.
Replacing the germanium with silicon in a transformerless design is unlikely to give you the distortion characteristics you may be seeking, but thats no reasong to stop experimenting, keep going!
Regards
Henry
The crazy thing is that not many years ago, you could walk into any electronics shop and buy exactly what you want off the shelf.
I built several amps for schoolfriends with these ready-built modules.
Andy
.
I built several amps for schoolfriends with these ready-built modules.
Andy
.
Thanks for the schematic Elvee. I've seen another schem using the TL431 some time ago. At the time I thought it would work as a headphone amp to practice with my guitar but it could be used to power a next stage.
Hi
You might have trouble with TIP31/32. These are bigger than you need for 1W, and have low gain. SO you need to increase the driver current.
I've made a very good 1W amp using BC307 (BC557)for the input, BC237 (BC547) for the driver and a bias stabiliser; and pairs of BC337/BC327 (two pairs) in the output. ONe pair should be enough but the gain roll-off is a little high at 500 mA, so sharing between two is better.
You could use a single pair of high gain high current Zetex (now Diodes) transistors but they will be more expensive than a couple of pairs of BC337/327.
John
You might have trouble with TIP31/32. These are bigger than you need for 1W, and have low gain. SO you need to increase the driver current.
I've made a very good 1W amp using BC307 (BC557)for the input, BC237 (BC547) for the driver and a bias stabiliser; and pairs of BC337/BC327 (two pairs) in the output. ONe pair should be enough but the gain roll-off is a little high at 500 mA, so sharing between two is better.
You could use a single pair of high gain high current Zetex (now Diodes) transistors but they will be more expensive than a couple of pairs of BC337/327.
John
Hi John, thank you for your suggestion.
The problem is that I didn't know what to use to replace the Germanium transistors in the original circuit and the TIP31/TIP32 sounded like a good choice. With the the current schematic the amp doesn't sound very good I had to increase the values of R7 and R9. The output transistors really need a heat sink as is referred in the Mullard's book.
Could you share the schematic? Thanks.
The problem is that I didn't know what to use to replace the Germanium transistors in the original circuit and the TIP31/TIP32 sounded like a good choice. With the the current schematic the amp doesn't sound very good I had to increase the values of R7 and R9. The output transistors really need a heat sink as is referred in the Mullard's book.
Could you share the schematic? Thanks.
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For the output NPN, a 2N3053 was the tranny of choice but I cannot remember it's complementary. ( something like a 2N2905 / BC160 would work ) Does not have to be "matched" and sound quality is not too important
for the input, BC107 or 2N2222 for the NPN, similar for the PNP 2N5401
andy
.
for the input, BC107 or 2N2222 for the NPN, similar for the PNP 2N5401
andy
.
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