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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: 31 Dec 2012, 15:15 
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Joined: 24 Feb 2009, 03:24
Posts: 562
Location: USA
If Your amplifier is parallel SE, current 50 ma for every tube is small to provide good sound. I understand You why You don't like its sound. These tubes sound good with big current.
You can adjust every current to 80-100 ma per tube. Common cathode resistor must be about 200-220 ohm/10 Watts. Your output transformer must be with current more 250 ma. I don't know what kind is Yours..../that is, maybe, another beer in Your wishes/.
/And change, please, ECC803... and computers "cathode" shunt caps, these are not for Audio/.

_________________
Hi End is back proportional to the number of composite parts!
Projects: OTL 6AS7 Gen, Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, PP 6005 Gen. Ellectric , headphone ampl. OTL Loftin White 6AS7 RCA....SE E84L& E80CC Siemens&Tel-n.
http://azazello-sound.blogspot.com/


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PostPosted: 01 Jan 2013, 10:39 
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Joined: 19 Mar 2012, 19:22
Posts: 168
Location: Wales, UK
Hi,

Thanks for your advice. So just to clarify I need to:-

1. Adjust the cathode resistors so that each tube runs at around 80 - 100ma. Cathode resistors need to be around 200 - 220 ohms.
2. Change the cathode capacitors for audio grade items.
3. Change ecc803 for something else like a ecc82/12au7?

My output transformers currently are not rated at 250ma but I am planning on buying better quality items such as edcor so I will make sure that the primary is rated for 250ma.

Many thanks for your help.

Phil


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PostPosted: 01 Jan 2013, 13:54 
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Joined: 24 Feb 2009, 03:24
Posts: 562
Location: USA
3....ECC81 /12AT7/ or ECC85/heating is different/ is good choice. If You will use ECC82 /12AU7/, gain will be small more than 2 times. You can use E180F, E186F in triod mode, 6S45P, with gains about 50, but with cool sound.
Upgrade for two channels will be expensive, but choice is Yours....

_________________
Hi End is back proportional to the number of composite parts!
Projects: OTL 6AS7 Gen, Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, PP 6005 Gen. Ellectric , headphone ampl. OTL Loftin White 6AS7 RCA....SE E84L& E80CC Siemens&Tel-n.
http://azazello-sound.blogspot.com/


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PostPosted: 02 Jan 2013, 17:40 
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Joined: 19 Mar 2012, 19:22
Posts: 168
Location: Wales, UK
Hi

Thanks for that. I might start with changing the cathode caps and changing the preamp stage circuit to use a different tube and then I will change the output transformers last as they will most probably be the most expensive items.

Many thanks,

Phil


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PostPosted: 12 Feb 2013, 18:39 
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Joined: 19 Mar 2012, 19:22
Posts: 168
Location: Wales, UK
It's been over a month scince I started trying to change the tonal qualities of the amp and so far it's coming along nicely. High frequencies no longer suffer from harshness and low frequencies have good deffinition and solidity. The midrange also no longer sounds harsh, except for when low quality recordings are played. I have changed the resistors and capacitors for good quality items instead of the cheap parts that were originally inside the amp.

Changes that I haven't done yet are:-

1. Raise the idle current on the output tubes, idle current is at 50 - 55mA per tube. Would like to raise the current to roughly 80 - 100mA. Output transformers will need to be changed before I do this.

2. Change the circuit slightly so that I can use a 12au7 instead of a 12ax7

3. Bypass cathode caps with 0.1uF polypropylene capacitors

So far I am quite happy with the sound but I was wondering if there is a way to make the midrange frequencies sound less forward or is it something that SE amplifiers do?

Many thanks

Phil


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