I am looking at making a Hi-Fi valve amp. Though I have a
backround in electronics, valves are completely new to me.
Some general comments please.
I would like to use something like this -
preamp - 12AX7
PA driver - 12AU7 (is this enough?)
Power Amp - KT88 or 6550C x2 (push-pull)
all x2 for stereo.
Is this feasable?
What do you think of the valve selection?
I have not seen any ciruits that use this combination.
I have seen some circuits, but I would like some ideas.
I can run the filaments for all these tubes from 6.3V,
AC or DC? some think AC, others DC - what reasons?
Layout seems to be very important, why - hum?
Earthing too, but I have read that some people have hum
no-matter how carefully they wire it.
I was thinking of a solid state power supply but someone
said they are noisy. A 5AR4 will not deliver enough
current, can they be paralleled?
I have seen some photos of nice wooden chassis, do they
need to be shielded?
I need to do bulk research.
Any comments would be helpful.
you will certainly get at lot of alternative suggestions
on your choice of tubes (everybody have their favos)
but I think you have made right decision on that
they are "mainstream" tubes, easy to find and replace
and a lot of knowledge is around of how they behave
and how they should be designed for
Good Luck
on your choice of tubes (everybody have their favos)
but I think you have made right decision on that
they are "mainstream" tubes, easy to find and replace
and a lot of knowledge is around of how they behave
and how they should be designed for
Good Luck
VALVE CHOICES
Hi,
Just to give some short answers:
Too much gain and one of the least linear triodes so that's a no go from me.
Probably not.You are going to do the phase splitting with the other half of the twin triode?
Why not.
AC.
See:http://www.diyaudio.com/forums/showthread.php?s=&threadid=6082
Shouldn't be a problem with PP amps and IHT.
You could use a pair of GZ34 in a Graetz bridge configuration.
If you don't suffer from severe RFI then there is no need for shielding.
Ciao,
Hi,
Just to give some short answers:
Too much gain and one of the least linear triodes so that's a no go from me.
Probably not.You are going to do the phase splitting with the other half of the twin triode?
Why not.
AC.
See:http://www.diyaudio.com/forums/showthread.php?s=&threadid=6082
Shouldn't be a problem with PP amps and IHT.
You could use a pair of GZ34 in a Graetz bridge configuration.
If you don't suffer from severe RFI then there is no need for shielding.
Ciao,
I would try something a little different for the 1st two stages. AX7 and AU7 are so over used.. try something intresting.
and besides, they look kinda goofy next to a big 6550
AC on the heaters (output tubes at least)
you can put them on the gain tubes if you want.. i dont think its needed.
I often tell people to try AC first, DC if AC hums.
maybe try a 5U4.. they got what.. 250mA DC out?
or, if you want to try something neat, try a pair of damper diodes..
and besides, they look kinda goofy next to a big 6550
AC on the heaters (output tubes at least)
you can put them on the gain tubes if you want.. i dont think its needed.
I often tell people to try AC first, DC if AC hums.
maybe try a 5U4.. they got what.. 250mA DC out?
or, if you want to try something neat, try a pair of damper diodes..
Some very quick replies, Thank you very much.
I have ordered this book -
Valve Amplifiers by Morgan Jones
http://www.amazon.com/exec/obidos/t...f=sr_1_1/102-0409407-0371358?v=glance&s=books
and judjing by the reviews, it is a good book to have.
I value your opinions, but let me defend my valve choices a bit -
- I would like to keep this simple and easy to build (i.e.- use parts that are easy to get hold of). The 'interesting' stuff can come later.
- These valves are current and common, and readily available. there are perhaps only 20 or so types i can get my hands on locally. perhaps suggest a common alternative?
- I have seen the first 2 stages in a number of circuits. Is this not a proven design?
some silly questions -
Colt45
If I play it safe and design with max values in mind, 4 x KT88's would be 900+ mA yes?
fdegrove
What is -
IHT
Graetz bridge (a standard bridge rectifier?)
Aren't the GZ34 and 5AR4 equivalents?
Thank you all and more comments please!
I have ordered this book -
Valve Amplifiers by Morgan Jones
http://www.amazon.com/exec/obidos/t...f=sr_1_1/102-0409407-0371358?v=glance&s=books
and judjing by the reviews, it is a good book to have.
I value your opinions, but let me defend my valve choices a bit -
- I would like to keep this simple and easy to build (i.e.- use parts that are easy to get hold of). The 'interesting' stuff can come later.
- These valves are current and common, and readily available. there are perhaps only 20 or so types i can get my hands on locally. perhaps suggest a common alternative?
- I have seen the first 2 stages in a number of circuits. Is this not a proven design?
some silly questions -
Colt45
If I play it safe and design with max values in mind, 4 x KT88's would be 900+ mA yes?
fdegrove
What is -
IHT
Graetz bridge (a standard bridge rectifier?)
Aren't the GZ34 and 5AR4 equivalents?
Thank you all and more comments please!
I know the name Morgan Jones.Robert-V said:
He has designed a little, interesting Headphones-Amp.
It uses E88CC/6DJ8 tubes. (is that 12AU or 12AX ?)
I wouldn't mind try to build that one.
Morgan Jones Tube Headphones Amplifier
Hey, nice to see another person interested in tubes. They're great for sure. About that ax7 and au7 config, well, those tubes, as was mentioned before are a little overused and not that linear. But for newbie purposes and to keep the work simplistic, an ax7 is fine and the sound will still be impressive. The KT88 is my personal favorite tube. British, high power, high fidelity, nice looking, inefficient, just perfect for audio. I don't think you totally need to have two gainstages though. Unless you were planning to use the au7 as a phase splitter or something. I find that the KT88 with one other medium gain tube is more than plenty gain, unless you use crazy amounts of negative feedback.
Just keep asking around and look at lot's of diagrams and notes. It's quite simple really to make a tube amp.
Hope you have good luck.
/Duo
Just keep asking around and look at lot's of diagrams and notes. It's quite simple really to make a tube amp.
Hope you have good luck.
/Duo
I've just been going through the same considerations for a KT88 based amp and as I davour simplicity I ended up thinking I would build one of Andrea Ciuffoli's designs
http://www.audiodesignguide.com/my/sekt88.html
Of course, life being what it is, my son, whose 14, decided he would like to build the amplifier.... so I've changed direction 'cos he needs a proven kit for his first project...
However the above design impressed me as very capable...what do the panel think?
James D.
http://www.audiodesignguide.com/my/sekt88.html
Of course, life being what it is, my son, whose 14, decided he would like to build the amplifier.... so I've changed direction 'cos he needs a proven kit for his first project...
However the above design impressed me as very capable...what do the panel think?
James D.
GRAETZ
Hi,
Indeed that's it.
One can use such rectification with tube diodes as well and since you wondered about current capability I suggested a pair of
GZ34/5AR4 in such a setup.
It will give you full wave rectification with higher current capability.
I do not hold the book you refer to so it's a bit hard to judge for me.
If however I find a copy of the circuit on the web I'll comment further.
Ciao,
Hi,
Indeed that's it.
One can use such rectification with tube diodes as well and since you wondered about current capability I suggested a pair of
GZ34/5AR4 in such a setup.
It will give you full wave rectification with higher current capability.
I do not hold the book you refer to so it's a bit hard to judge for me.
If however I find a copy of the circuit on the web I'll comment further.
Ciao,
I was a bit confused this morning.....
I meant Andrea Ciuffoli's design:
http://www.audiodesignguide.com/my/sekt88.html
I meant Andrea Ciuffoli's design:
http://www.audiodesignguide.com/my/sekt88.html
A NON-COMMERCIAL DIAGRAM
Hi,
Just what the doctor ordered?
Ciao,
Hi,
Just what the doctor ordered?
An externally hosted image should be here but it was not working when we last tested it.
Ciao,
John,
For the Andrea Cuiffoli design
Assuming my understanding is correct...(Big assumption) then the primary is fed as usual from the parallel anodes of the KT88s and the secondary is in series with the KT88's cathodes and the load. Thus the secondary and the load (the speaker) are applying local feedback to the output stage....
I haven't analysed the stage but that is my intuitive understanding from looking at the schematic. The output transformer is drawn back to front i.e. secondary first to simplify the drawing (but complicate the understanding ?)
I hope this is correct and that it helps!
James D.
For the Andrea Cuiffoli design
Assuming my understanding is correct...(Big assumption) then the primary is fed as usual from the parallel anodes of the KT88s and the secondary is in series with the KT88's cathodes and the load. Thus the secondary and the load (the speaker) are applying local feedback to the output stage....
I haven't analysed the stage but that is my intuitive understanding from looking at the schematic. The output transformer is drawn back to front i.e. secondary first to simplify the drawing (but complicate the understanding ?)
I hope this is correct and that it helps!
James D.
James,
Aha, I didn't notice the little arrrow downwards to show that the bottom of the secondary is grounded. Presumably the speaker is connected straight across the secondary, (although there is no indication), and the entire speaker drive is applied to the cathodes through the resistors.
Hmm, that'll make Ra (Rp) nice and low......waits for descenting followups...
He draws schematics even worse than me!
Thanks for the clarification.
Cheers,
Aha, I didn't notice the little arrrow downwards to show that the bottom of the secondary is grounded. Presumably the speaker is connected straight across the secondary, (although there is no indication), and the entire speaker drive is applied to the cathodes through the resistors.
Hmm, that'll make Ra (Rp) nice and low......waits for descenting followups...
He draws schematics even worse than me!
Thanks for the clarification.
Cheers,
John,
I believe you are correct - re-reading my message I was not clear that the speaker is connected across the secondary in the 'normal' manner but that is my understanding too.
Your 'lowers Ra (Rp)' comment is interesting! Note the load from the OPT primary is 2k3 which is as expected for parallel KT88 - so no indication that Ra is lowered... However I would expect the feedback around the output stage to lower Zo for the amplifier... I must get around to analysing this amp. I think it is a very interesting design and I should make the effort to understand it.
This one is nice too - as an alternative here is Andrea version of a two stage pp KT88 amplifier.
http://www.audiodesignguide.com/my/pp3.html
Ciao
James D.
I believe you are correct - re-reading my message I was not clear that the speaker is connected across the secondary in the 'normal' manner but that is my understanding too.
Your 'lowers Ra (Rp)' comment is interesting! Note the load from the OPT primary is 2k3 which is as expected for parallel KT88 - so no indication that Ra is lowered... However I would expect the feedback around the output stage to lower Zo for the amplifier... I must get around to analysing this amp. I think it is a very interesting design and I should make the effort to understand it.
This one is nice too - as an alternative here is Andrea version of a two stage pp KT88 amplifier.
http://www.audiodesignguide.com/my/pp3.html
Ciao
James D.
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