I am building this one, not for its sound quality for I haven't even heared one side yet, but for it's power and simple design with 6SN7's...
I am substituting the KT88's for EH KT90's...
Main points for me building this type are ultralinear and push pull apart from the Class-B? operation..
The modification that I'm doing to the power supply allows me to use one B+ transformer for two channels..
(thanks guys).
I've essentially just bolted myself onto this schematic and with half of the parts already here aint backing out just yet...
I intend to use the 'standard' transformers for the output and power supply however instead of Torodials, as I've heared bad things from using those...
http://www.plitron.com/pages/Products/Audio/vtvkt88.htm
I am substituting the KT88's for EH KT90's...
Main points for me building this type are ultralinear and push pull apart from the Class-B? operation..
The modification that I'm doing to the power supply allows me to use one B+ transformer for two channels..
(thanks guys).
I've essentially just bolted myself onto this schematic and with half of the parts already here aint backing out just yet...
I intend to use the 'standard' transformers for the output and power supply however instead of Torodials, as I've heared bad things from using those...
http://www.plitron.com/pages/Products/Audio/vtvkt88.htm
Hello Redwine, thanks for giving another choice. I like it because it looks simple ¿Have you tried it?
There are some things I don't understand at the first schematic. Maybe someone can help me
http://www.bonavolta.ch/hobby/en/audio/kt88_1.htm
- ¿What is the mission of the 1-1.5 nF/500V condenser at the plate of the KT88 and how do you adjust it?
- I don't understand how the power supply works. ¿Why the 380V come from the center tap of the 2x2,5V output?.
- ¿How do you adjust the 50 Ohm pots at the heater's outputs?
- The 100 uF/160V condenser at the KT88 is drawn as non-electrolythic. I assume it is electrolythic.
Thanks
There are some things I don't understand at the first schematic. Maybe someone can help me
http://www.bonavolta.ch/hobby/en/audio/kt88_1.htm
- ¿What is the mission of the 1-1.5 nF/500V condenser at the plate of the KT88 and how do you adjust it?
- I don't understand how the power supply works. ¿Why the 380V come from the center tap of the 2x2,5V output?.
- ¿How do you adjust the 50 Ohm pots at the heater's outputs?
- The 100 uF/160V condenser at the KT88 is drawn as non-electrolythic. I assume it is electrolythic.
Thanks
I don't understand how the power supply works. ¿Why the 380V come from the center tap of the 2x2,5V output?.
It has me quite puzzled as well and very worried!!! the windings of 2.5v 4a can NOT handle that current in the first place!??????????????????????
What the fudge is going on here?
Apart from the immense resistive load between each tap of the B+ tranny in the rectifier tube I can not see how in any rational form how this could possibly work with both a potential dead short and the 90 or so watts going through those poor little 10watt windings.
It has me quite puzzled as well and very worried!!! the windings of 2.5v 4a can NOT handle that current in the first place!??????????????????????
What the fudge is going on here?
Apart from the immense resistive load between each tap of the B+ tranny in the rectifier tube I can not see how in any rational form how this could possibly work with both a potential dead short and the 90 or so watts going through those poor little 10watt windings.
typical circuit
It is a typical full wave center tap power supply with a 5 volt CT winding which is where the B+ should be taken from. The 4A filament winding is fine for a 5u4 tube, so no current problems. The input filter seems a little large, so I would be careful.
The capacitor at the plate of the KT88 is an air variable most likely. That does concern me as one shouldn't be necessary in a good design.
Try to limit the feedback from stage to stage through the power supply if possible as this is a weak area.
It is a typical full wave center tap power supply with a 5 volt CT winding which is where the B+ should be taken from. The 4A filament winding is fine for a 5u4 tube, so no current problems. The input filter seems a little large, so I would be careful.
The capacitor at the plate of the KT88 is an air variable most likely. That does concern me as one shouldn't be necessary in a good design.
Try to limit the feedback from stage to stage through the power supply if possible as this is a weak area.
Layberinthius said:
Because the schematic use a tube rectifier...and the 5volts AC feed the rectifier heaters/cathode...and as usually with tube rectifiers the output rectified dc come from the heaters/ cathode.
But if they handle 4 Amps...who needs more???...if the rectifier don't even output 500 mA DC
Take some reading about tube recifiers...this one is a classic circuit!
Hi,
No, not tone but phase response and resonance correction.
It is set to correct phase according to the type/brand of OPT used.
For those amongst you not in possesion of "L'Audiophile # 14" , the circuit is also described in "Selection de L"AUDIOHILE Tome 1
L"Electronique", ages 87 and onwards.
Note that this is all written in French of course.
Cheers,
No, not tone but phase response and resonance correction.
It is set to correct phase according to the type/brand of OPT used.
For those amongst you not in possesion of "L'Audiophile # 14" , the circuit is also described in "Selection de L"AUDIOHILE Tome 1
L"Electronique", ages 87 and onwards.
Note that this is all written in French of course.
Cheers,
Hi,
1) I believe simple is the best. So simple circuit design usually sounds good.
2) If possible, the circuit without negative feedback will sound more musical.
3) From my understanding, for the variable 1 - 1.5 nF capacitor,
usually it will be quite common in RF amplifier circuit. It is used to prevent high frequency feedback to power supply unit.
4) One more simple design for 6550, KT88, KT90
1) I believe simple is the best. So simple circuit design usually sounds good.
2) If possible, the circuit without negative feedback will sound more musical.
3) From my understanding, for the variable 1 - 1.5 nF capacitor,
usually it will be quite common in RF amplifier circuit. It is used to prevent high frequency feedback to power supply unit.
4) One more simple design for 6550, KT88, KT90
Attachments
materials used etc.
The materials used in making a variable capacitor are very poor sounding, steel, brass etc. And the capacity is quite high, from its stated value.
Opps I see it is mica. But 1000pf - 1500 pf is enormous, if I read it correctly. The output capacitance of the tube is only around 10-15pf plus a little stray.
Looks to me that something is really wrong if that kind of capacity is necessary.
The materials used in making a variable capacitor are very poor sounding, steel, brass etc. And the capacity is quite high, from its stated value.
Opps I see it is mica. But 1000pf - 1500 pf is enormous, if I read it correctly. The output capacitance of the tube is only around 10-15pf plus a little stray.
Looks to me that something is really wrong if that kind of capacity is necessary.
Hi,
O.K....Once more, the 1500 pF varicap serves to linearise the performance of the OPT beyond 80 KHz.
This, combined with the 7dB NFB loop and the excellent bandwidth of the SRPP gives you an amp that's linear from 10 HZ-100KHz @ 1W.
Do away with the NFB and you'll see the sensitivity rise to 0.55V as opposed to 1V, distortion increases to ~3% at 10W, BW decrease to 50KHz and so on.
Note that the Tango U808 is a 50W SE model chosen for a 10W amp.
I hope this helps,
O.K....Once more, the 1500 pF varicap serves to linearise the performance of the OPT beyond 80 KHz.
This, combined with the 7dB NFB loop and the excellent bandwidth of the SRPP gives you an amp that's linear from 10 HZ-100KHz @ 1W.
Do away with the NFB and you'll see the sensitivity rise to 0.55V as opposed to 1V, distortion increases to ~3% at 10W, BW decrease to 50KHz and so on.
Note that the Tango U808 is a 50W SE model chosen for a 10W amp.
I hope this helps,
I see
I see Frank. Didn't see the above 80khz previously. Didn't realize that that much capacity is needed that high.
Quick question Frank. Since the inductance varies with signal level, is there a particular procedure you like for adjusting the value of capacitance or is it a matter of adding some capacitance helps?
Thanks Frank.
ps. I need to go back to bed I think, all my corrections here. Up too late last night.
I see Frank. Didn't see the above 80khz previously. Didn't realize that that much capacity is needed that high.
Quick question Frank. Since the inductance varies with signal level, is there a particular procedure you like for adjusting the value of capacitance or is it a matter of adding some capacitance helps?
Thanks Frank.
ps. I need to go back to bed I think, all my corrections here. Up too late last night.
Hi,
I just use a frequency sweep of 1KHz to 15KHz at varying power, 5mW to 5W.
The reason a varicap is suggested here is that it leaves the possiblity of other brands of OPTs open.
If the OPT comes with a frequency response graph and you know the primary inductance, you have a good starting point.
Good night.
Cheers,
I just use a frequency sweep of 1KHz to 15KHz at varying power, 5mW to 5W.
The reason a varicap is suggested here is that it leaves the possiblity of other brands of OPTs open.
If the OPT comes with a frequency response graph and you know the primary inductance, you have a good starting point.
Good night.
Cheers,
That 1-1.5 nF variable is a mica compression capacitor. They are compact, some 1/2" by 1" or so. They are common in power amplifiers for VHF transmitters.
An air variable with max 1500pF for these voltages is HUGE.
Compression trimmers can be found as surplus:
http://www.surplussales.com/Variables/Compression/CompCap1.html
An air variable with max 1500pF for these voltages is HUGE.
Compression trimmers can be found as surplus:
http://www.surplussales.com/Variables/Compression/CompCap1.html
Am I wrong or ZurLindes pentode version using OPT without UL tap??? (http://www.bonavolta.ch/hobby/en/audio/kt88_2.htm)
How much power can it produce?
Anyone around here build it actually?
How much power can it produce?
Anyone around here build it actually?
back on line
Jax, yes, I use to use them when working rf, but I thought the voltage rating was only around 500 volts, if that. Maybe some higher voltages available?
I still don't like the materials used, at least the ones I use to use.
Seemed like, as I recall, steel tabs to solder to. Any copper in them now?
If one doesn't change OPTs, maybe get the exact value and purchase fixed cap?
Jax, yes, I use to use them when working rf, but I thought the voltage rating was only around 500 volts, if that. Maybe some higher voltages available?
I still don't like the materials used, at least the ones I use to use.
Seemed like, as I recall, steel tabs to solder to. Any copper in them now?
If one doesn't change OPTs, maybe get the exact value and purchase fixed cap?
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