Help! is this work?

[radio28]

Help is this schematic work What is the performance of this kt88 pp circuit? How can I modify it? Any comment/ opinion is welcomed. I'm sorry to the poor picture qualilty

 

[radio28]

here it is...

 

[Giaime]

Ehm... in the picture the input stage looks very fuzzy, I can't really see... and the power supply section is visible only for a part... you should try to post a link to a full size image.

I can't see any obvious flaws on it, thought... it seems professionally designed, even if I don't recall what particular amp it refers to... seems good.

edit: C11 on the power supply seems to be missing, it's replaced by a wire. Obviusly it must be replaced by the proper capacitor that C11 is referring to.

Pretty much simple triode/UL operation switch...

 

[radio28]

Thank you Giaime, I noticed that C11 is missed in the schematic, I think it should be connected just like C12.

Some friend told me that I can swap the input 12ax7 with 12at7 and have a better result , is this work?

This is the one with full power supply circuit

 

[Giaime]

A 12AU7/AT7 will work, althought with lower gain. Since the whole amp is enclosed in a feedback loop (look at the wire from the secondary of the output trasformer to the cathode of the first tube), I would try to put a lower gain tube in place of the 12AX7 and disconnect the feedback loop. This in general make better musical results, at the expense of distortion. See what you prefer best: with feedback or without. But remeber that if you use feedback it would be better to put a 12AX7 in the first stage; otherwise the amp wouldn't have much gain to feedback.

 

[radio28]

I am surprise that 12ax7, 12at7 and 12au7 can be swapped freely and no need to change the related RC components value

I know KT88 and 6550 is about the same, but can I swap the kt88s to el34s?

Since it sounds like that this amp doesn't have enough gain, is it better if I add a pre-amp (say marantz 7 circuit) between CD player and this amp?

Is that the kt88s in the schematic connected in UL mode now? That switch is used to change the kt88 in triode/UL operation, right?

Thank you very much

 

[Giaime]

I am surprise that 12ax7, 12at7 and 12au7 can be swapped freely and no need to change the related RC components value

No. In theory you have to do the math and recalculate some values: in practice were a circuit is designed to make hi-gain out of a 12AX7, replacing it with a 12AU7 or 12AT7 will lead to a circuit that performs in similar ways, although at lower gains. A 5751 instead can replace a 12AX7 with no changes, also for lower gain. So in approssimation yes, you can swap them out.

I know KT88 and 6550 is about the same, but can I swap the kt88s to el34s?

KT88 and 6550 is not the same... look at the datasheets. And no, you cannot replace KT88 with EL34: they are different tubes (even in pinout: el34 is a real pentode instead Kt88 is a tetrode) with different plate and screen power handling. You can replace the el34 with kt88 in most of the cases (given that you rebias the amp), but the inverse is not possible and not good for the tubes and the amp.

Since it sounds like that this amp doesn't have enough gain, is it better if I add a pre-amp (say marantz 7 circuit) between CD player and this amp?

How can you say that the amp hasn't enought gain? Have you already built it? Looking at the schematics it seems that you can drive it directly with a CD player...

Is that the kt88s in the schematic connected in UL mode now? That switch is used to change the kt88 in triode/UL operation, right?

Yes, exactly. In the schem the KT88 are connected UL, the switch can make them work as triodes (screen connected to plate).

 

[huymdt]

Please help me
I bought an amplifier it the same above and I have a problem!
It has two way signals input (convert to 1.volume or 2.direct). With signals direct (used volume from CD) it's ok, but signals input through the 1. error... The volume transmit signals minimum at level 1/16 and get the maximum at level 1/15 (it seem not boundary between min and max).

I used the 6Pi3C-E tube instead of KT88. The voltage pinout:
- The anode (pin 3) = 390 VDC
- The g2 (pin 4) = 390 VDC
- The g (pin 5) = -26 VDC
- The ht (pin 2 & 7) = 5,8 VAC
- The cathode (pin 8) = 0,9 VDC
Is it good with my amplifier?

Thanks

 

[amperex]

Mullard 12AX7 input to a Sylvania 6SN7GT with 'T' shaped plates gets my vote.

 

[huymdt]

Please help me
I bought an amplifier it the same above and I have a problem!
It has two way signals input (convert to 1.volume or 2.direct). With signals direct (used volume from CD) it's ok, but signals input through the 1. error... The volume transmit signals minimum at level 1/16 and get the maximum at level 1/15 (it seem not boundary between min and max).

I used the 6Pi3C-E tube instead of KT88. The voltage pinout:
- The anode (pin 3) = 390 VDC
- The g2 (pin 4) = 390 VDC
- The g (pin 5) = -26 VDC
- The ht (pin 2 & 7) = 5,8 VAC
- The cathode (pin 8) = 0,9 VDC
Is it good with my amplifier?

Thanks

pls show me an instructions... with above level voltages can I replace with 6V6-GTY tube now?