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#26 pre amp

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Thanks Salas, I'm testing the concept with a cheap 5842 spud , figure if the Salas HVSS works with that it would work with this, always get ahead of my self though :)

Have heard before that SSHV marries with a Spud. Is it doing OK on yours? No active reg with some gain and BW must be asked for feeding such an inductive & swinging power load if not heavily cut in internal bandwidth. Then it will lose quality though. There will be things that can't marry. But its nice to try pairings.
 
I should have it put together in a week or so, Quanghao reported success with 6c45pi spud, and I think someone else also, To drive my headphones I only need max 1V (30mW) tested with a 1khz sine wave at about twice my normal listening (this is only 12V on the primary), I'm optimistic but my pre-filtering prior to the HVSS is such that if it doesn't work I can just remove the HVSS and add a 50 uf cap and probably be OK. I'm also going conservative with 4x10k grid stoppers and a cathode stopper.
 
I should have it put together in a week or so, Quanghao reported success with 6c45pi spud, and I think someone else also, To drive my headphones I only need max 1V (30mW) tested with a 1khz sine wave at about twice my normal listening (this is only 12V on the primary), I'm optimistic but my pre-filtering prior to the HVSS is such that if it doesn't work I can just remove the HVSS and add a 50 uf cap and probably be OK. I'm also going conservative with 4x10k grid stoppers and a cathode stopper.

and the good CCS pretty much means you can get away without a top notch PS.
 
Its simple. If you use a 30mA anode CCS on your audio circuit, the local reg's CCS has to be set higher, so to provide for the audio circuit's consumption plus 20-25mA minimum for its own reg use. So check the voltage drop on your reg's CSS setting resistor, divide it by its value, and know first of all that there is enough current. We should know before going further.

Salas, I found the problem BTW. The SSHV was not controlling the voltage because the IRF 840 got opened for some reason:). After I replaced it, everything came back to normal. As you said, I checked the current on anode CCS which is at 9ma and SSHV is at 40ma. Is this the optimal to operate? Now the pre amp is more silent without any speaker rumbling, but I felt the overall gain reduced significantly as well as it lost the liveliness of the music it had with anode chokes. I assume this is because the reduced gain hence any advice to fine tune and increase the gain?
 
A CCS should give as high a gain as possible, may want to check your cathode bypass cap. Or possibly your voltage drop across the CCS is not high enough to keep it from clipping, what is the voltage drop across the CCS (in-out of CCS)?

Regal, I think the issue is the latter; there is not enough voltage drop. What are the possible reasons for this?
 
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I want to try out battery bias with 26 - not in a preamp but the first stage of my SET. The preamp stage before it is a 10Y into a Hammond 126C OPT which I'm going to put on the same chassis as the amp. So I can use the secondary of the 126C for the battery bias to the 26.

So fill me in here as a battery bias beginner for what I need to do
- Do I need one battery or two, one per channel?
- If one battery, do I use it via a 1 meg resistor to each grid or what?
- If two batteries do I again use a resistor or just connect it straight to the grid? What value resistor
- What kind of battery is it best to use?
- Anything else I should know?

Just occurred to me that with a transformer secondary, the grid and earth are connected so that would drain the battery, so I need a cap somewhere?

andy
 
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can help?
 

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Hi nicoch46

That's helpful. The first diagram is new to me - I didn't know you could place the battery in series. How does that sound?

The second diagram is the one I need I think. I can see you don't need a cap here since it's open circuit when the tube is off. So presumably no resistor between battery and transformer if the diagram is to be believed.

That looks like you'd need one battery for each channel?

andy
 
diyAudio Chief Moderator
Joined 2002
Paid Member
Salas, I found the problem BTW. The SSHV was not controlling the voltage because the IRF 840 got opened for some reason:). After I replaced it, everything came back to normal. As you said, I checked the current on anode CCS which is at 9ma and SSHV is at 40ma. Is this the optimal to operate? Now the pre amp is more silent without any speaker rumbling, but I felt the overall gain reduced significantly as well as it lost the liveliness of the music it had with anode chokes. I assume this is because the reduced gain hence any advice to fine tune and increase the gain?

Having 31mA more, gives good reg's output impedance. I consider 20-25mA extra as adequate and always must allowed, so your excess is nice. As for best anode load I consider anode choke, electronic gyrator, CCS, in subjectively descending order. A CCS gives more gain than a resistor but sometimes less than a choke.
 
Here's my quick first draft of a schematic where the 26 is the second stage with battery bias - please make any comments or corrections.

I'm not sure if this comes out landscape or portrait - the original is landscape but sometimes my attachments get turned around. Can anyone explain what to do?

andy
 

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Having 31mA more, gives good reg's output impedance. I consider 20-25mA extra as adequate and always must allowed, so your excess is nice. As for best anode load I consider anode choke, electronic gyrator, CCS, in subjectively descending order. A CCS gives more gain than a resistor but sometimes less than a choke.

Thanks Salas. Even I prefer the anode chokes but when it comes to noise, it is terrible compared to others as I observed. I have pretty decent anode chokes done by EP but still when it comes to the larger output coupling cap (in order to get the optimal low frequency), it is bit of problem to use those chokes. It seems like that there is no way out to have both the larger caps and chokes together without this compromise.:(
 
Andy here's what I have tested so far which was recommended by Kevin.

- Do I need one battery or two, one per channel? One per channel.

- If one battery, do I use it via a 1 meg resistor to each grid or what?
- If two batteries do I again use a resistor or just connect it straight to the grid? What value resistor?
Refer the schematic attached.

-Just occurred to me that with a transformer secondary, the grid and earth are connected so that would drain the battery, so I need a cap somewhere? Probably you could refer Kevin's article in PF. (http://www.positive-feedback.com/Issue16/kennedy.htm). I have seen a very informative discussion on this topic in one of the DIY site which I couldn't find the link (I think it was a Philippines or Malaysian site. Remember "ArnoldC" was active there so it could most probably a Philippines). Check if you could locate it.

- What kind of battery is it best to use? I tried few of different types but Alkaline came to top comparing the sonics.


Hope this info. helps.
 

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