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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 23 Dec 2018, 19:23 
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Joined: 24 Nov 2010, 14:39
Posts: 31
Location: California
Hmmm 6AQ5....I remember reading somewhere that the 6AQ5 and 6V6 are electrically similar. Any chance that 6V6's (or the cheap 12V6 NOS) tubes could be effective in this design?


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PostPosted: 23 Dec 2018, 19:51 
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Joined: 06 Apr 2009, 10:08
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Location: US Pacific Northwest
Jim_O wrote:
Any chance that 6V6's (or the cheap 12V6 NOS) tubes could be effective in this design?
Yup.

The 6V6, 7408, 12V6, 6005, & 6669 can all be used in any circuit calling for the 6AQ5 (filament wiring allowed, of course).

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PostPosted: 24 Dec 2018, 09:54 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi Yes, in fact I have a boatload of 6005s (AKA industrial/rugged 6AQ5) to try in it. Stay tuned for a while as I won't be able to get it done for a few days or so because of the holidays.

How about a SE KT120 headphone amp? Just Kidding. Everyone have a great holiday and new year.

Good listening
Bruce

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PostPosted: 24 Dec 2018, 12:20 
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Joined: 02 Mar 2009, 12:41
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Location: Vänersborg, Sweden
The 6AQ5 is a great tube. Very much like 6BQ5 on a diet. I have one stored away as I sold the mains transformer, salvaged from a Heatkit amp. I used a design from Frank Nachbaur.

Another similar tube with the same (?) data is the Russian 6N1P and the Chinese 6N1, but only packed in the more available noval package. I think there a a zillion different (or the same) headphone amps based on 6N1.

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PostPosted: 24 Jan 2019, 11:52 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi Everyone, Still working on a higher power version, but got side tracked to alter the original.

This is a bit of a departure for my projects and the long term upgrades to them. This headphone amp is rather nice (IMO) as it was posted but I figured it might be improved. With the indicated power supply it can have enough residual hum to be barely audible with sensitive headphones. Mine did. So hating hum as much as I do it seemed appropriate to reduce it. Using conventional techniques I could not completely eliminate it. So…having a penchant for doing “odd” things I decided to go to a non-conventional power supply. I used a 120VAC to 12VDC SMPS to power the whole thing. The 12VDC was for heaters and to power a variable voltage output SMPS that could deliver 50-400VDC at up to 200ma depending on the output voltage. I was quite happy with 50ma at 140 volts. The HV SMPS did have noise, but not what was expected. The noise was fairly wide band low frequency hiss. There was some high frequency noise, but that was easy to fix. I tried a number of things and finally settled on a choke (1.5H) input to 330uf capacitor as filtering devices. This worked perfectly. The S/N in the PS at the tube output transformer input was at -85db wideband. It is a very quiet power supply. The hum at the headphone jack is gone. So…it is a cheap solution and in a number of ways better. The HV SMPS is available from a number of sellers and there are two versions. I used the dual voltage output one as it was cheaper and easier to get. The single output one differs in that it has one less rectifier, filter and uses the boost transformer windings differently. Either will work fine. A WEB search for it should find them easily. Qunison and Smakn are the brands I found. Hook up is simple and they work well. Voltage stability is excellent. Certainly worth a try. I posted the schematic and some photos to show the project.

Good listening
Bruce
Attachment:
Headphone 1.jpg
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Headphone 2.jpg
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Headphone 3.jpg
Attachment:
Headphone 4.jpg
Attachment:
New Headphone Power Supply.jpg


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PostPosted: 04 Feb 2019, 09:48 
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Joined: 09 Aug 2018, 03:15
Posts: 20
Location: Forsbacka Sweden
I have built this one and it works really great. In my country we have 220V AC and we from time to time use transformers to reach 110V and USA made equipmet. Is it possible to make an powersupply with that transformer? A transformer that transforms 220V to 110V 100W. Have it rectified and smoth and drive the headphone amp with an decent output?
Why? They are cheap and available.

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PostPosted: 04 Feb 2019, 15:21 
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Location: Arizona, USA
Hi, I would think that ought to be fine. 110 rectified and filtered would be about 150VDC, just right. The heaters will still need power, but low voltage transformers are usually cheap too. BTW you only need about 15 watts not 100.

Good listening
Bruce

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PostPosted: 06 Feb 2019, 21:32 
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Location: Arizona, USA
Hi Everyone, I am making progress on the preamp's big brother. It is using a SMPS like the updated schematic of the one a few posts above. Just a bigger one able to handle (it says) up to a 70 watt load. Good thing as initial guess for B+ load is about 35 watts at 200 VDC. I'm anticipating a clean output of about 1.5 watts. I am making it usable for headphones or speakers. The phone output will be reduced to about 100mw max. A nice desk top unit. Final selection of tubes (so far ) is 6F5P / 6GV8 / ECL 85. Push-pull class A U/L into 10K anode to anode. It could deliver more power as I have used these tubes in a prototype amp and got 4 watts out, but that is overkill for a headphone amp and makes the power input needs greater than I think possible with the SMPS. It also tends to increase the residual noise level ...something that is unacceptable. I will most likely submit it as a separate project on the site.

Good listening
Bruce

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PostPosted: 08 Feb 2019, 01:07 
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Joined: 09 Oct 2012, 19:43
Posts: 334
Location: Vancouver Canada
I've been looking for one of the SMPS high-voltage supplies but no find on Amazon .CA or .COM. Do you have any more info on the one you used?


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PostPosted: 08 Feb 2019, 09:37 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, Here are some links

https://www.amazon.com/Voltage-Converte ... eature_div

https://www.ebay.com/itm/8-32V-to-45-39 ... 100623.m-1

https://www.ebay.com/itm/121652391983

Good listening
Bruce

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