Does the amplifier work correctly now?
It seems to be working, but how much power does it put out?
With efficient horn speakers, it should play relatively loud, but not if for some reason it has gain that is too low, and not if its total output power is 10dB low (like 300mW instead of 3Watts).
I would think that full scale peaks out of a CD player would cause that (properly working) amplifier to put out 3 Watts.
I use a Denon Audio Test CD, which has a number of full scale sine waves at various frequencies.
Use a scope and Load resistor to do full power out testing, do not use speakers (steady full power sine waves could be bad for the horn speakers, such testing will certainly be uncomfortable, if not also damaging, to your ears).
An accurate schematic of all the wiring and parts values you have now would be a real good start.
And some measurements of DC voltages would be helpful.
Before modding an amplifier, it is good to check that it is working properly first.
That way, if there is a mistake in modifying, the only cause is usually the modifictions, not the original parts and circuit.
(Chase one tail, do not chase two tails at once).
It seems to be working, but how much power does it put out?
With efficient horn speakers, it should play relatively loud, but not if for some reason it has gain that is too low, and not if its total output power is 10dB low (like 300mW instead of 3Watts).
I would think that full scale peaks out of a CD player would cause that (properly working) amplifier to put out 3 Watts.
I use a Denon Audio Test CD, which has a number of full scale sine waves at various frequencies.
Use a scope and Load resistor to do full power out testing, do not use speakers (steady full power sine waves could be bad for the horn speakers, such testing will certainly be uncomfortable, if not also damaging, to your ears).
An accurate schematic of all the wiring and parts values you have now would be a real good start.
And some measurements of DC voltages would be helpful.
Before modding an amplifier, it is good to check that it is working properly first.
That way, if there is a mistake in modifying, the only cause is usually the modifictions, not the original parts and circuit.
(Chase one tail, do not chase two tails at once).
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Sage advice 6A3s, I know that rabbit hole very well! 🙂
The amp works well with no extraneous noises, but SQ is not great. The midrange is recessed and IMO the amp should sound better than it actually does with my Klipsch Heresy 3s (99db/w).
My original plan was to convert to 2A3, but it's a lot of work (and knowledge) required for this and I have since found out that the 6B4G is supposed to be a very good-sounding valve if properly run. Perhaps you guys can confirm or rebutt this please?
The amp works well with no extraneous noises, but SQ is not great. The midrange is recessed and IMO the amp should sound better than it actually does with my Klipsch Heresy 3s (99db/w).
My original plan was to convert to 2A3, but it's a lot of work (and knowledge) required for this and I have since found out that the 6B4G is supposed to be a very good-sounding valve if properly run. Perhaps you guys can confirm or rebutt this please?
I can read a schematic, but have never drawn one in my life and wouldn't have a clue.
I will be checking voltages again and will post them.
I will be checking voltages again and will post them.
6B4G and 2A3 should sound better with low ripple DC filament supplies (no 100Hz sidebands on the musical tones; as long as the B+ ripple is low too).
But 1 Amp DC per 6B4G, versus 2.5A 2A3 filament requires some different filament transformers. And they should be separate windings, to allow separate self bias RC networks.
Actually, I used the 6B4G "sister" tube, the 6A3, just the same, except 4 pins instead of the 8 pins you have now.
I did use DC powered 6A3 filaments.
If I ever build a Direct Heated Triode (DHT) amplifier again, it will only be the 2.5V filament tubes, and use a DC filament supply. With DC on 2.5V filaments have a more even spread of plate current across the plate surface, than 5V (300B) and 6.3V DHT filaments.
I will use either 2A3, or 45 tube (1.5A filament) types.
I have used 2A3 and 45 tubes before, but this time I will use DC powered filaments, not AC powered filaments.
I hope you can get some help and recommendations, and look at the tradeoffs, and difference of parts and work required to come up with a good plan of what modifications, circuit, and tubes to use.
Then, happy modifying, and happy listening!
But 1 Amp DC per 6B4G, versus 2.5A 2A3 filament requires some different filament transformers. And they should be separate windings, to allow separate self bias RC networks.
Actually, I used the 6B4G "sister" tube, the 6A3, just the same, except 4 pins instead of the 8 pins you have now.
I did use DC powered 6A3 filaments.
If I ever build a Direct Heated Triode (DHT) amplifier again, it will only be the 2.5V filament tubes, and use a DC filament supply. With DC on 2.5V filaments have a more even spread of plate current across the plate surface, than 5V (300B) and 6.3V DHT filaments.
I will use either 2A3, or 45 tube (1.5A filament) types.
I have used 2A3 and 45 tubes before, but this time I will use DC powered filaments, not AC powered filaments.
I hope you can get some help and recommendations, and look at the tradeoffs, and difference of parts and work required to come up with a good plan of what modifications, circuit, and tubes to use.
Then, happy modifying, and happy listening!
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Well, considering my youngest kid is two years older than I am, joining at -1 is easy 😀
But I must admit, 7 is close: 7^2 😛
@Barrymidd
Genuine SE 6B4s need DC heating. With good hum control technique, AC heating of SE 2A3s is acceptable.
Other than filament voltage and basing, the 6B4 and 2A3 are "identical". Therefore, changes to the small signal circuitry are not required, should you switch O/P tube types.
Mediocre or worse SQ may, unfortunately, reflect the quality of the O/P "iron" present. "The 'iron' makes the amp." You can't turn dung into gold. The other way around is easy enough. "Been there, done that."
If you decide on a 2A3 swap, I suggest you contact Sowter or other "nearby" winder for a custom filament trafo that contains a pair of CT 2.5 VAC windings. The CTs will simplify hum management. Just connect a winding to a filament and use the CT for the self bias network/ground connection. You avoid chassis modification, for the installation of hum balance potentiometers.
Genuine SE 6B4s need DC heating. With good hum control technique, AC heating of SE 2A3s is acceptable.
Other than filament voltage and basing, the 6B4 and 2A3 are "identical". Therefore, changes to the small signal circuitry are not required, should you switch O/P tube types.
Mediocre or worse SQ may, unfortunately, reflect the quality of the O/P "iron" present. "The 'iron' makes the amp." You can't turn dung into gold. The other way around is easy enough. "Been there, done that."
If you decide on a 2A3 swap, I suggest you contact Sowter or other "nearby" winder for a custom filament trafo that contains a pair of CT 2.5 VAC windings. The CTs will simplify hum management. Just connect a winding to a filament and use the CT for the self bias network/ground connection. You avoid chassis modification, for the installation of hum balance potentiometers.
Thanks Eli
Plan of attack is to wire the amp up properly and get it running properly (if I move to 2A3 then I will get a mains transformer wound to spec first) and then upgrade the output transformers. I know I need new iron for good results and have had a main transformer wound by a British company before for an Audio research which worked very well.
Hopefully someone can tell me the specs for the tranny I need whenI have made my decisions re. valves.
Plan of attack is to wire the amp up properly and get it running properly (if I move to 2A3 then I will get a mains transformer wound to spec first) and then upgrade the output transformers. I know I need new iron for good results and have had a main transformer wound by a British company before for an Audio research which worked very well.
Hopefully someone can tell me the specs for the tranny I need whenI have made my decisions re. valves.
Regulated DC Filament Power Supply
A quick note, for what it's worth: I used Pete Millett's DC power supply board on my Mono Vinyl Flexi-SET Amp, which takes everything from a 46 tetrode to a 300B (yup, two sockets).
I used it for easy switching between different filament voltages, but of course the DC eliminates the dreaded DHT hum, too, which has been an ISSUE for me for 20 years.
I still use a Heathkit IP-32 regulated PS and fixed bias. At very least I need to move the WIRES around to the back (three little grandkids, another on the way), but ideally need to build a dedicated unit. NAH, who am I kidding, that ain't gonna happen in this lifetime.
[NB I am 67yo, so YET ANOTHER mid-boomer blowing things up.]
Usually available on eBay. IIRC, there was a Mouser parts list available.
I have filament voltage test ports on the top and a nice (ALPS?) pot to adjust the filament voltage. Works a treat, as my British cousins would say.
Don't recall the amperage, but I remember being surprised how high it was.
HOWEVER, it does like input voltage greater than output voltage (nothing's free), so for 6.3VDC out you might have to tie together a 5V and a 6V. For the old triodes/tetrodes, I could use a 6.3V tap.
Here's a photo...
A quick note, for what it's worth: I used Pete Millett's DC power supply board on my Mono Vinyl Flexi-SET Amp, which takes everything from a 46 tetrode to a 300B (yup, two sockets).
I used it for easy switching between different filament voltages, but of course the DC eliminates the dreaded DHT hum, too, which has been an ISSUE for me for 20 years.
I still use a Heathkit IP-32 regulated PS and fixed bias. At very least I need to move the WIRES around to the back (three little grandkids, another on the way), but ideally need to build a dedicated unit. NAH, who am I kidding, that ain't gonna happen in this lifetime.
[NB I am 67yo, so YET ANOTHER mid-boomer blowing things up.]
Usually available on eBay. IIRC, there was a Mouser parts list available.
I have filament voltage test ports on the top and a nice (ALPS?) pot to adjust the filament voltage. Works a treat, as my British cousins would say.
Don't recall the amperage, but I remember being surprised how high it was.
HOWEVER, it does like input voltage greater than output voltage (nothing's free), so for 6.3VDC out you might have to tie together a 5V and a 6V. For the old triodes/tetrodes, I could use a 6.3V tap.
Here's a photo...
Attachments
240V/6.3V (adjustable) DC filament power supplies are available from Ebay Europe for £25ish each, so does anyone have experience of these? Will make most of my mains trans redundant but is a simple (on paper) solution. 1 for each 6B4G and 1 for both 6SN7s.
How does that sound?
How does that sound?
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