Hi , I have an old Hammond Output transformer (123D) that i don"t know the specs of and was wondering if there is a way for me to figure out the Winding Ratio/Impedances using my DMM ??
I contacted hammond and they said that it doesn"t show up in any of their cataloges and don"t know anything about it ....
I got it off a homemade tube amp that I found in a junk pile that didn"t work , it had really old and obscure Japanese tubes in it (One recifier tube and triode and a pentode) and the Power transformer was also japanese (it had 90v and 100v primary taps) ......
The output transformer has a primary(2 wires) and 2 secondaries (2 wires and places to solder 2 more numbered 1 - 4)
I was hoping to use it in a 6V6 power amp project .....
Thanx guys .......
I contacted hammond and they said that it doesn"t show up in any of their cataloges and don"t know anything about it ....
I got it off a homemade tube amp that I found in a junk pile that didn"t work , it had really old and obscure Japanese tubes in it (One recifier tube and triode and a pentode) and the Power transformer was also japanese (it had 90v and 100v primary taps) ......
The output transformer has a primary(2 wires) and 2 secondaries (2 wires and places to solder 2 more numbered 1 - 4)
I was hoping to use it in a 6V6 power amp project .....
Thanx guys .......
Yes.
You have already figured out the winding connections and figured out that the primary will have more windings, thinner wire and higher resistance.
With a low voltage AC source (AC wallwart/variac/filament transformer/transformer from cheap junked SS gear) and your DMM you can find the voltage aka winding ratio, and thus (by squaring that ratio) the impedance ratio.
Google:'measuring output transformer impedances'
Remember that the OT is an 'impedance reflector' , so the speaker impedance and the connections you choose for the speaker, control the impedance reflected back to the tube hanging on the primary.
I have a 1972 Hammond catalog home but I don't found the 123D, it must be very old ... Usually a 6V6 or 6AQ5 SE 4,5 watts amplifier with 250V plate and screen grid supply need a 5000 ohms transformer, it is easy to find out if your 123D is suitable for that project.Hi , I have an old Hammond Output transformer (123D) that i don"t know the specs of and was wondering if there is a way for me to figure out the Winding Ratio/Impedances using my DMM ??
I contacted hammond and they said that it doesn"t show up in any of their cataloges and don"t know anything about it ....
I got it off a homemade tube amp that I found in a junk pile that didn"t work , it had really old and obscure Japanese tubes in it (One recifier tube and triode and a pentode) and the Power transformer was also japanese (it had 90v and 100v primary taps) ......
The output transformer has a primary(2 wires) and 2 secondaries (2 wires and places to solder 2 more numbered 1 - 4)
I was hoping to use it in a 6V6 power amp project .....
Thanx guys .......
Just hook-up the primary of the 123D (with no load) to the secondary of a little low voltage transformer, measure the voltage at the primary and at the secondary (also between the unused taps if you like). Then divide the primary voltage by the secondary one, this will give you the voltage ratio to 1 of the transformer ... The impedance ratio is the square of the voltage ratio, just multiply it by your speaker impedance to see what impedance you will have at the tube plate.
One of the secondary wire must be a common and the two unused taps must be for other speakers impedances, most of those four wires secondary transformers was made for 4, 8 and 16 ohms (when all the taps go to the same winding). For a 6V6 you need a 5000 to 8 ohms, that mean you need a voltage ratio of the square root of ( 5000 / 8 ) = 25 : 1.
For example, with your test setup, if you read 12 volts on the primary and 0,48 volts at the secondary, you have a 12 / 0,48 = 25 : 1 voltage ratio and it is just perfect for your project. Now, suppose you have 15 volts at the primary and 0,85 volts at the secondary, 15 / 0,848 = 17,689 ... For a 8 ohms speaker, the impedance ratio is 8 x the square of 17,689 = 2503,2 ohms ... It is good for a 50C5 or a 2A3 power triode $$$ but much too low for a 6V6 ... But for a 16 ohms speaker, 16 x the square of 17,689 = 5006,4 ohms, that mean it is a 16 ohms tap for a 5000 ohms transformer ...
Good luck with your project !
Alain.
Hi , Are those numbers accurate ?? (Sorry my math is awefull) ....
I just hooked up the Transformer to a 12.3v AC source , First I connected it backwards (oops) and got 350v AC on the output , then connected it the proper way and got 0.48v AC which is exactly what you said it should be for a 6v6 amp .....
So Did i just get lucky ??
It is actually a quite large transformer , about 3x as big as the one in a different 6v6 amp i have ......
Thanx
The math is pretty straightforward- just follow Alain's calculation.
12.3/0.48 is about 25.6- which is the voltage or windings ratio.
Square 25.6 and you get (25.6*25.6=657) the impedance ratio.
So, whatever impedance you hang on the secondary will be multiplied by 657 to the primary. 8 ohm speaker will reflect about 5.3k to the primary, 16 ohm speaker will reflect 10.6k etc....
Were both secondary windings the same?
12.3/0.48 is about 25.6- which is the voltage or windings ratio.
Square 25.6 and you get (25.6*25.6=657) the impedance ratio.
So, whatever impedance you hang on the secondary will be multiplied by 657 to the primary. 8 ohm speaker will reflect about 5.3k to the primary, 16 ohm speaker will reflect 10.6k etc....
Were both secondary windings the same?
Yes you are lucky !
8 x square of ( 12,3 / 0,48 ) = 5253 ohms ... It is perfect for your 6V6 project ! Notice the impedance don't have to be exact, +/- 5 % is OK, even +/- 10% is acceptable ... There is also some power loss in every transformers and the speakers impedance vary a lot anyway, at the resonance frequency, a 8 ohms speaker can have over 50 ohms impedance and more than 16 ohms at high frequency ...
Hammond make transformers since almost 80 years, they "know how", since your transformer is bigger than average one's, you will get very good bass because the DC magnetic saturation will be lower. I use Hammond transformers very often since 40 years for projects and replacements, some Montreal store near my village sale them, a good thing to save on shipping but they are a bit expensive.
The 5000 ohms SE transformers was very common, they can be use with a lot of tubes types like the beampowers or pentodes 6AQ5, 6BQ5, 6GK6, 6L6, 807, 5881, 7408, 6550, power triodes like 50, 300B, 211, SV572-3, SV572-10, SV811-3 and many "dissimilar twin triodes" made for B&W TV Vertical-Deflection Oscillator and Amplifier, they sound very good and are not very expensive ... You can also use two tubes requiring 10000 ohms in parallel, this will double their power ...
Take care with high voltages, they can hurt or even kill you ...
Cheers,
Alain.
Last edited:
I didnt actually test the other secondary winding , I measured one primary and got the right volatges so I stopped there , but I will because I would like to be able to connect a 4 ohm or 16ohm speaker .......
I just finnished building a 2 channel guitar amp , it had 2 x 12ax7 per channel preamp with a 3 band tone controll all running at 300v DC going into a lm3886 chip and I used a couple 5v relays to build the switching circuit activated by a footswitch and it has a couple LED"s to show what channel is in use , and it has an effects loop .....
Another question , I have this 115v in 115v out ac power transformer and was wondeing if it would be possible to use a voltage doubler with it to get 300v ish DC for the 6v6 ??
I think the transformer can probably put out about at least 500 ma .... And I think the 6v6 only needs like 45 - 50 ma ......
Thanx
Yes.
Grab a free copy of PSUD (PSU designer) from Duncan amps site- it's a great tool for simulating PS circuits. It showed 290v out of a 115VAC transformer, when I checked just now.
Now that caps are cheap (and compact) doubler circuits make a lot of sense and can use up iron from the parts box. You could even put a couple of bell transformers (or filament transformers) back-to-back if you didn't have a 115/115 transformer.
If you are interested using a voltage doubler, you must know there is two kinds of them, "full wave" and "half wave". I make the next Spice simulation many months ago to see the differences between them.
This "equivalent" circuit is for 120V supply and 250ma load and the DC output is more than 290V ... If your transformer give you 115V and your maximum load is around 60ma, you can get easely about 290V like VictoriaGuy said or even more than 300V, it depend on the value of the electrolytic capacitors. That is more than enought because the datasheet's of the 6V6 say the typical operation with a 5000 ohms transformer need 250V between plate, screen grid and the cathode ... You have to take care the dissipation don't exceed the maximum of 14 watts for the plate and 2,2 watts for the screen grid or your 6V6 will toast ...
There are some parts in the circuit just for the simulator, they are not there in the real circuit ... The 10 ohms resistor represent the resistance of the transformer windings or current limiting resistor for direct AC line operation (dangerous), the two circles represent the DC load, it is a constant current symbol, the 100n capacitor and 100k resistor are just there to measure the ripple with Probe2-NODE ... The only "real parts" you need are the diodes and the electrolytic capacitors.
The ripple of the two doublers are about the same but not at the same frequency ... You will have to use a good filtering anyway, a choke or a resistor follow by another electrolytic capacitor. Personnally, I prefer the "half wave" one because the "working voltage" of the capacitors can be 200V, the "full wave" need 350V one's but the final ripple will be a bit lower at 120 Hz than at 60 Hz with the same second filtering capacitor.
When you evaluate the supply voltage you need, you have to calculate the voltage drop on the primary winding of the output transformer, if the current is 45ma (with no signal) and the DC resistance of the primary is 100 ohms for example, the voltage drop across the primary will be 100 x 0,045 = 4,5 volts.
If you use a autobias resistor (and a coupling capacitor of 100 or 220uF 25V) for the 6V6 (that is the best), for a -12,5V bias, since the current with no signal of the plate plus the screen grid is about 50ma, you need a 12,5 / 0,05 = 250 ohms resistor (2 or 3 watts OK). Of course, the voltage drop across this resistor is 12,5 volts ...
So you need a supply voltage of 250 + 4,5 + 12,5 = 267 volts ... If your supply give you 290 volts, you need a resistor in the filtering circuit with a voltage drop of 290 - 276 = 14 volts ... The current is 50ma plus the current of the driver tube, let said 2 ma, a total of 52 ma, the resistor have to be 14 / 0,052 = 269,23 ohms (270 ohms is OK) and is dissipation is 14 x 0,052 = 0,728 watts, so a 2 or 3 watts resistor will not heat too much ...
I hope I don't all confuse you with those details but they are important to get the right voltages for the tube. This is just an example but if you like to design your amplifier completely, it is not very difficult. If you use the typical operation of the datasheets, you will have no problems, just add a high-mu driver/preamp like a 6AV6 or a 12AX7 triode and you will have a lot of gain, add a - 6dB negative feedback and wou will have a much lower distortion.
Here's a good 6V6 GTA datasheet from RCA
Here's the important part for your project, I put red rectangles around what is important for you, notice the 4,5 watts is the one that use a 5000 ohms transformer !
If you have any questions about all that, I will be happy to help you, the DIY part I prefer since 40 years is the design and maths ...
Have a good day !
Alain.
This "equivalent" circuit is for 120V supply and 250ma load and the DC output is more than 290V ... If your transformer give you 115V and your maximum load is around 60ma, you can get easely about 290V like VictoriaGuy said or even more than 300V, it depend on the value of the electrolytic capacitors. That is more than enought because the datasheet's of the 6V6 say the typical operation with a 5000 ohms transformer need 250V between plate, screen grid and the cathode ... You have to take care the dissipation don't exceed the maximum of 14 watts for the plate and 2,2 watts for the screen grid or your 6V6 will toast ...
There are some parts in the circuit just for the simulator, they are not there in the real circuit ... The 10 ohms resistor represent the resistance of the transformer windings or current limiting resistor for direct AC line operation (dangerous), the two circles represent the DC load, it is a constant current symbol, the 100n capacitor and 100k resistor are just there to measure the ripple with Probe2-NODE ... The only "real parts" you need are the diodes and the electrolytic capacitors.
An externally hosted image should be here but it was not working when we last tested it.
The ripple of the two doublers are about the same but not at the same frequency ... You will have to use a good filtering anyway, a choke or a resistor follow by another electrolytic capacitor. Personnally, I prefer the "half wave" one because the "working voltage" of the capacitors can be 200V, the "full wave" need 350V one's but the final ripple will be a bit lower at 120 Hz than at 60 Hz with the same second filtering capacitor.
When you evaluate the supply voltage you need, you have to calculate the voltage drop on the primary winding of the output transformer, if the current is 45ma (with no signal) and the DC resistance of the primary is 100 ohms for example, the voltage drop across the primary will be 100 x 0,045 = 4,5 volts.
If you use a autobias resistor (and a coupling capacitor of 100 or 220uF 25V) for the 6V6 (that is the best), for a -12,5V bias, since the current with no signal of the plate plus the screen grid is about 50ma, you need a 12,5 / 0,05 = 250 ohms resistor (2 or 3 watts OK). Of course, the voltage drop across this resistor is 12,5 volts ...
So you need a supply voltage of 250 + 4,5 + 12,5 = 267 volts ... If your supply give you 290 volts, you need a resistor in the filtering circuit with a voltage drop of 290 - 276 = 14 volts ... The current is 50ma plus the current of the driver tube, let said 2 ma, a total of 52 ma, the resistor have to be 14 / 0,052 = 269,23 ohms (270 ohms is OK) and is dissipation is 14 x 0,052 = 0,728 watts, so a 2 or 3 watts resistor will not heat too much ...
I hope I don't all confuse you with those details but they are important to get the right voltages for the tube. This is just an example but if you like to design your amplifier completely, it is not very difficult. If you use the typical operation of the datasheets, you will have no problems, just add a high-mu driver/preamp like a 6AV6 or a 12AX7 triode and you will have a lot of gain, add a - 6dB negative feedback and wou will have a much lower distortion.
Here's a good 6V6 GTA datasheet from RCA
Here's the important part for your project, I put red rectangles around what is important for you, notice the 4,5 watts is the one that use a 5000 ohms transformer !
An externally hosted image should be here but it was not working when we last tested it.
If you have any questions about all that, I will be happy to help you, the DIY part I prefer since 40 years is the design and maths ...
Have a good day !
Alain.
Last edited:
Sorry, I make a really stupid mistake in that paragraph ... I gest I was a bit tired and I don't notice I invert the "6" and the "7" ... It happen very often when I try to type too fast ... Probably a form of dyslexia ...
Here's what you should read with underlined corrections in green :
I is alway better to "double check" everything ...
Cheers,
Alain.
Here's what you should read with underlined corrections in green :
I is alway better to "double check" everything ...
Cheers,
Alain.
You filter will be a CRC because the first capacitor is already in the voltage doubler ... But the value of the resistor depend of how much voltage will give you your transformer and voltage doubler and how much voltage drop you will have across the primary of your output transformer ... 440 ohms is just an example if you have 190 DC and if you need 267 volts supply (depending of the output trandformer), you will have to ajust the value of that resistor to get the right voltage for the 6V6.
You will also have to measure the DC resistance of the primary of your output transformer to find out what gona be the voltage drop across it, you can do that right now with your multimeter ... You will have to use the "ohm law" to calculate the values of the resistors and different powers, voltages and currents in the circuit. The basic formulas you can use to calculate the circuits are :
E = R x I ... voltage = resistance x current
E = P / I ... voltage = power / current
E = √ ( P x R ) ... voltage = square root of ( power x resistance )
I = E / R ... current = voltage / resistance
I = P / E ... current = power / voltage
I = √ ( P / R ) ... current = square root of ( power / resistance )
P = E x I ... power = voltage x current
P = R x I ² ... power = resistance x square of current
P = E ² / R ... power = square of voltage / resistance
In these formulas :
E = voltage in volts (V)
I = current in amperes (A)
R = resistance in ohms
Don't forget 1A = 1000ma and 1ma = 0,001A
Also 1K = 1000 ohms, 1M = 1000K or 1000000 ohms
So 1 ohm = 0,001K and 1K = 0,001M
Similary for the capacitors in micro-farads (uF), nano-farads (nF) and picofarad (pF) :
1 uF = 1000 nF = 1000000 pF and 1 nF = 0,001 uF = 1000 pF ...
Those formulas are suitable for DC or AC ( peak or RMS ) but you cannot mix DC, AC peak and AC RMS in the same formulas ... This is a little more complicated and I prefer not explain all that to you right now, you will be all mixed up ... It took many weeks for an average electronic student to learn all the basic of DC and AC electricity ...
For now, just measure the DC resistance of the primary of your 5K output transformer and tell me the result.
I will draw this weekend the simplest (but good) circuit you can use for your amplifier, I can do that really fast with my electronic drawing softwares ...
I like to know what you like to use this amplifier for, a monophonic sound system or a musical instrument amplifier ?
You said you use to build a guitar amplifier, what kind of guitar do you play and what kind of music ... Lead, accompaniment, bass, all of them ? Jazz, rock, metal, classic, western ?
I ask you that because there are specials ways to build an amplifier depending the kind of instrument and the type of music you play. For example, all the rock lead guitarists I know love the sound of the old "fender twin reverb" ... Bassman like very much the Marshall sound with a big woofer, etc ... Of course, with 4,5 watts, you will not get a lot of decibels but you can get a sound you will like using a high efficiency loudspeaker.
Don't worry about the time it took me to explain those thing to you, I also do it for the thousands of peoples who visit this forum and are interested in small tubes amplifiers design ... I alway like to be a professor before and it is a way for me to do it ... I also have to practice my english writing because I am writing my own electronic DIY web site and it will be bilingual, french and english ...
Cheers,
Alain.
My output transformer has a Resistance of just under 500 ohms (486ohms) ....
I used a CRCLCRC in the Guitar amp that I just finnished but I had a lot more voltage to drop in that project .....
I was going to measure the output volatge and calculate the dropping resistor based on the output Voltage and calculate in the resistance of the ouput transformer to find the value of the dropping resistor ......
Ive got a couple old 470uF 200V caps and about 8 100uF 250v Caps that I will be using and I have a bunch 1n4007 diodes and lots of power resistors ...
I know my ohms law fairly well (I use a calculator cuz it is quicker for me ) and have built maybe 20 amps but all have been solidstate accept for a couple tube preamps , have even designed a few simple solid state circuits like Mic preamps and guitar pedals and some studio monitors , guitar amps ect , but tubes are pretty foreign to me so im on a pretty steep learning curve here so I really appriciate the help and from a fellow canuck ..
I"ll probably be useing it with a guitar preamp in front of it so it"s not a hi fi sound I"m looking for ......
Thanx again .....
I used a CRCLCRC in the Guitar amp that I just finnished but I had a lot more voltage to drop in that project .....
I was going to measure the output volatge and calculate the dropping resistor based on the output Voltage and calculate in the resistance of the ouput transformer to find the value of the dropping resistor ......
Ive got a couple old 470uF 200V caps and about 8 100uF 250v Caps that I will be using and I have a bunch 1n4007 diodes and lots of power resistors ...
I know my ohms law fairly well (I use a calculator cuz it is quicker for me ) and have built maybe 20 amps but all have been solidstate accept for a couple tube preamps , have even designed a few simple solid state circuits like Mic preamps and guitar pedals and some studio monitors , guitar amps ect , but tubes are pretty foreign to me so im on a pretty steep learning curve here so I really appriciate the help and from a fellow canuck ..
I"ll probably be useing it with a guitar preamp in front of it so it"s not a hi fi sound I"m looking for ......
Thanx again .....
Last edited:
Oh ! 486 ohms is very high for a output transformer, the voltage drop will be about 22 volts ...My output transformer has a Resistance of just under 500 ohms (486ohms) ....
I used a CRCLCRC in the Guitar amp that I just finnished but I had a lot more voltage to drop in that project .....
I was going to measure the output volatge and calculate the dropping resistor based on the output Voltage and calculate in the resistance of the ouput transformer to find the value of the dropping resistor ......
Ive got a couple old 470uF 200V caps and about 8 100uF 250v Caps that I will be using and I have a bunch 1n4007 diodes and lots of power resistors ...
I know my ohms law fairly well (I use a calculator cuz it is quicker for me ) and have built maybe 20 amps but all have been solidstate accept for a couple tube preamps , have even designed a few simple solid state circuits like Mic preamps and guitar pedals and some studio monitors , guitar amps ect , but tubes are pretty foreign to me so im on a pretty steep learning curve here so I really appriciate the help and from a fellow canuck ..
I"ll probably be useing it with a guitar preamp in front of it so it"s not a hi fi sound I"m looking for ......
Thanx again .....
That's a good thing you got lots of power resistors, you will have to try many and serie/parallel combinations of them to find the perfect dropping resistance. Your 470uF 200V electrolytics are perfect for a "halfwave voltage doubler" but the working voltage of your 100uF 250V is a bit too low for a tube amplifier, the best for that amplifier is 350V ...
You will also need a 6,3 VAC transformer at least 1A for the tubes heater's of this amplifier, preferably with a "center tap" unless it is better to use a 200 ohms or more hum balancing trimpot. But if you have a 10 VAC transformer or a little more with a "center tap", you can make a DC supply to feed the heaters at 6,3 VDC ... You will have less hum this way. You can also use a 12,6 VAC 500ma or more transformer with a "center tap" or not, there are many possibility.
I made a Spice simulation of the amplifier I think about with a 6V6 and a 6AV6 and it look very good, low distortion and excellent frequency response, I will be back with that, update with the 486 ohms transformer ... It is possible to use many of your 100uF 250V for this amplifier, a pair in series is the same as a 50uF 500V ...
Cheers,
Alain.
Hi , Yes I know that the Transformer has a Pretty high resistance as it is a pretty big transformer......
I used the Same 100uF 250v Caps in series/paralell with my 2 ch tube preamp project ..... I used 8 in all (400uF) with that PSU and a 10H choke in the middle and I elevated the heaters to about 30v and it was a pretty quiet PSU ..... I was going to try to elevate the heaters again with this project , maybe referance them to the Cathode of the 6v6 ......
Well I"m off camping for the weekend , and thanx again ......
Cheers
I used the Same 100uF 250v Caps in series/paralell with my 2 ch tube preamp project ..... I used 8 in all (400uF) with that PSU and a 10H choke in the middle and I elevated the heaters to about 30v and it was a pretty quiet PSU ..... I was going to try to elevate the heaters again with this project , maybe referance them to the Cathode of the 6v6 ......
Well I"m off camping for the weekend , and thanx again ......
Cheers
Hi Minion,
I hope you have a nice camping weekend, here in Quebec, it was very rainy ...
Like I promise, here's the Spice simulation results and the complete schematic of a good 6V6GT power amplifier with a 6AV6 driver I just finish designing, the 6AV6 have the same caracteristics as one triode of the 12AX7. I also work on many other projects this weekend, a push-pull class AB1 stereo amplifier using 6080 twin power triodes and a 2206CP based multifunctions frequency generator because my antique Hewlett Packard 205AG have some mysterious bad contacts problems and two weak tubes very hard to find (metal 6FS5GA).
I own many old scopes, one of them is a Tektronix 545A, it is defective since many years and contain 71 tubes ... I open it to verify what kind of tubes it contain, I have a big surprise because 69 are very good for audio projets, two big 6080 but also twenty-two 6DJ8 from Amperex ... A fantastic HIFI preamp twin triode, the equivalent of the well know 6N1P from Russia and China ... I will borrow tubes from this scope for my amplifiers tests for sure ...
Here's the Spice simulation schematic of the amplifier :
As you can see, I design it with the capacitors you tell me you got in stock and I use the highest voltage it is possible to obtain with a voltage doubler with a 115 VAC transformer, 332V, that's why the voltage dropping resistor R9 is 900 ohms. Of course, I don't think you can get a so high voltage from your supply and you will have to use a much lower value to get 285V on the other side ...
I put a zener diode to help stabilising the 263V for the 6V6 screen grid - which current raise a lot at full power - and the 6AV6, you don't have to use it absolutely but I think it's better. You can use a 27 or 28 volts from 0,5W to 10W but I think the bigger is the better, some suitable types are :
BZD2327 (27V 2,5W), BZT0327 (27V 3,25W), BZX79A27 (27V 0,5W), 1N4750 (27V 1W), 1N5361 (27V 5W), 1N5362B (28V 5W) and many more.
Notice at full power, the 6V6 current and bias drop instead raising, that's because the raise of the screen grid current and is voltage drop, it is worse without the zener ... The 6dB global negative feedback help attenuate the distorsions and to get a better lower bass response ... Here's the best frequency response you can get from this amplifier :
Here's now the complete amplifier schematic, I hope I don't forget anything :
You can find many 6V6 amplifiers schematics on Internet but I design this one specifically for your particular antique Hammond 123D output transformer, so if you build it, don't forget to tell me what are the results.
In the meantime, if you like to ask me any questions about all that, feel free to do it, if you are happy, I will be happy too !
Cheers,
Alain.
I hope you have a nice camping weekend, here in Quebec, it was very rainy ...
Like I promise, here's the Spice simulation results and the complete schematic of a good 6V6GT power amplifier with a 6AV6 driver I just finish designing, the 6AV6 have the same caracteristics as one triode of the 12AX7. I also work on many other projects this weekend, a push-pull class AB1 stereo amplifier using 6080 twin power triodes and a 2206CP based multifunctions frequency generator because my antique Hewlett Packard 205AG have some mysterious bad contacts problems and two weak tubes very hard to find (metal 6FS5GA).
I own many old scopes, one of them is a Tektronix 545A, it is defective since many years and contain 71 tubes ... I open it to verify what kind of tubes it contain, I have a big surprise because 69 are very good for audio projets, two big 6080 but also twenty-two 6DJ8 from Amperex ... A fantastic HIFI preamp twin triode, the equivalent of the well know 6N1P from Russia and China ... I will borrow tubes from this scope for my amplifiers tests for sure ...
Here's the Spice simulation schematic of the amplifier :
An externally hosted image should be here but it was not working when we last tested it.
As you can see, I design it with the capacitors you tell me you got in stock and I use the highest voltage it is possible to obtain with a voltage doubler with a 115 VAC transformer, 332V, that's why the voltage dropping resistor R9 is 900 ohms. Of course, I don't think you can get a so high voltage from your supply and you will have to use a much lower value to get 285V on the other side ...
I put a zener diode to help stabilising the 263V for the 6V6 screen grid - which current raise a lot at full power - and the 6AV6, you don't have to use it absolutely but I think it's better. You can use a 27 or 28 volts from 0,5W to 10W but I think the bigger is the better, some suitable types are :
BZD2327 (27V 2,5W), BZT0327 (27V 3,25W), BZX79A27 (27V 0,5W), 1N4750 (27V 1W), 1N5361 (27V 5W), 1N5362B (28V 5W) and many more.
Notice at full power, the 6V6 current and bias drop instead raising, that's because the raise of the screen grid current and is voltage drop, it is worse without the zener ... The 6dB global negative feedback help attenuate the distorsions and to get a better lower bass response ... Here's the best frequency response you can get from this amplifier :
An externally hosted image should be here but it was not working when we last tested it.
Here's now the complete amplifier schematic, I hope I don't forget anything :
An externally hosted image should be here but it was not working when we last tested it.
You can find many 6V6 amplifiers schematics on Internet but I design this one specifically for your particular antique Hammond 123D output transformer, so if you build it, don't forget to tell me what are the results.
In the meantime, if you like to ask me any questions about all that, feel free to do it, if you are happy, I will be happy too !
Cheers,
Alain.
Last edited:
Wow , thats pretty awesome and I will build it , it just might take me a while to get it finnished , My last project took 8 months to finnish ......
Would there be a problem dropping the Tube stage at the front end ??
Thanx again , I will post back with any problems/questions as I progress ..... i"m gona try to start on this PSU this week ......
Cheers
Would there be a problem dropping the Tube stage at the front end ??
Thanx again , I will post back with any problems/questions as I progress ..... i"m gona try to start on this PSU this week ......
Cheers
Last edited:
My projects often take many years, I am not in a hurry for DIY, it's just for fun and electronic learning ... The best ideas comme with time, one morning, you can wake up with a simple one you never have before and wonder how come !Wow , thats pretty awesome and I will build it , it just might take me a while to get it finnished , My last project took 8 months to finnish ......
Would there be a problem dropping the Tube stage at the front end ??
Thanx again , I will post back with any problems/questions as I progress ..... i"m gona try to start on this PSU this week ......
Cheers
About your question :
Would there be a problem dropping the Tube stage at the front end ??
I don't talk english very well and I am not sure I understand what you mean ... Do talk about not using the 6AV6 ?
If that is your question, you better not because you need over 8V RMS at the grid of the 6V6 to get the maximum power and you need the 6AV6 for the feedback loop, the gain of this tube in that cicuit is over 35.
May be you mean using a lower supply voltage for the 6V6, in that case, it is possible but everything will have to be calculated again and you will loss some power, at 180V from cathode to plate and screen grid, a 6V6 deliver only 2 watts ...
Cheers,
Alain.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.