Just for interest,
I find this inspires me:
otl amp.handmade with 12 PL36 tubes per channel . - YouTube
Thinking about Maida reg on the pre/driver..
Just waiting to see what Mr Murre finds with his regulators..
Think he could have extruded the wire and wound a Tx by hand ..
perhaps he is!!
Regards
M. Gregg
I find this inspires me:
otl amp.handmade with 12 PL36 tubes per channel . - YouTube
Thinking about Maida reg on the pre/driver..
Just waiting to see what Mr Murre finds with his regulators..
Think he could have extruded the wire and wound a Tx by hand ..
perhaps he is!!
Regards
M. Gregg
Current-drain on the driver/pre rail is pretty low, and wont significantly alter with signal.
I very much doubt there will be any significant change in regulating that supply, providing its got good filtering to start with!....
That otl on utube, Looks to have a LOT more PL36 than 12!
More like 16 or 20 if you count 'em! There's 4 rows of at Least 4 valves under those fans...
I very much doubt there will be any significant change in regulating that supply, providing its got good filtering to start with!....
That otl on utube, Looks to have a LOT more PL36 than 12!
More like 16 or 20 if you count 'em! There's 4 rows of at Least 4 valves under those fans...
It’s interesting that the pre/driver supply can be heard through the speaker. I know this because HT off Heaters Off in power stage.. yes still very quiet but you can hear it pull the pre supply fuse and its gone. Not surprising because the supply goes via feedback through 150 Ohm and speaker coil.
LOL And yes not significant gain to be had their me think's.I think it would be interesting to look at the main PSU ripple. .Space may be a problem..Mr Murre lets hear the outcome....
Alastair, I can agree it is very rugged. Power off all heaters switch the HT pull the 6c33c's while warm plug them back in, pull them again..OK i had power off!
Switch in and out heaters one or two or none and back on again!
Might try bypassing the choke with a .1uF it worked well in the past!
Some different bypass caps on order!
And yes I am convinced OTL...No Tx!
Regards
M. Gregg
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Decoupling filter-caps..
Using 0.1uF film caps to de-couple the filter cap supplying the pre stages should be a good idea, and if you have a larger value, up to 10uF may be good.
The two 'heavy' supplies for the O/P stage prob need around 25uF film-caps to amke any significant differences sonically....
--Even then, The effect will probably be minimal, but if you have them, might as well shove 'em in there...
Using 0.1uF film caps to de-couple the filter cap supplying the pre stages should be a good idea, and if you have a larger value, up to 10uF may be good.
The two 'heavy' supplies for the O/P stage prob need around 25uF film-caps to amke any significant differences sonically....
--Even then, The effect will probably be minimal, but if you have them, might as well shove 'em in there...
Just for fun link..
Servicing of a Musician OTL Hi-Fi Amplifier
Normal service will be resumed ASAP
Regards
M. Gregg
Servicing of a Musician OTL Hi-Fi Amplifier
Normal service will be resumed ASAP
Regards
M. Gregg
Seems like a good idea but my gut reaction is there won't be enough inductance to be any real use. I've got a 12VA 12-0-12 very similar - I'll test it later when I get this sick pair of Quad II's off my bench. I did once use the 2 x 110V primaries of this same tx as a line level isolator - it worked surprisingly well.
Simon
Simon
I have tried it a couple of times it depends on application..The only thing I did not see mentioned was that quite a high voltage can appear on the disconnected primary inder some conditions so they need insulating...
Just thought it might be interesting..
Regards
M. Gregg
Alastair..
Just thinking out loud here..
While after 4hrs listening to the OTL with Deadmau5 (for want of a better name)
deadmau5 "16th hour" - YouTube
Got to test the bass haven't you..
Shakes my laptop across the table.. and hammers the Alpairs into submission
Very deep bass....anyway..yes there are fuses and bypass caps just not on this pic...
Some discussion going on....
Sounds great!!
Regards
M. Gregg
Just thinking out loud here..
While after 4hrs listening to the OTL with Deadmau5 (for want of a better name)
deadmau5 "16th hour" - YouTube
Got to test the bass haven't you..
Shakes my laptop across the table.. and hammers the Alpairs into submission
Very deep bass....anyway..yes there are fuses and bypass caps just not on this pic...
Some discussion going on....
Sounds great!!
Regards
M. Gregg
Attachments
Opening titles, 'Lethal Weapon III' also demo the bass capabilities fairly well....
The original Sting track doesnt contain the added LF portions, so it must be the film itself....
Its one of the items I use for checking....
Pretty sure as I recall (Will have to confirm...) That the CT of the mains Tx is connected to the centre-point of the caps, (ie--direct, no 1K resistor) in my amp...
Been thinking of trying those 12V 50VA tx I have as chokes on the two lines, although the hum isnt a problem with mine--Just out of curiosity....
The original Sting track doesnt contain the added LF portions, so it must be the film itself....
Its one of the items I use for checking....
Pretty sure as I recall (Will have to confirm...) That the CT of the mains Tx is connected to the centre-point of the caps, (ie--direct, no 1K resistor) in my amp...
Been thinking of trying those 12V 50VA tx I have as chokes on the two lines, although the hum isnt a problem with mine--Just out of curiosity....
Alastair,
I am waiting for some coupling caps at the moment..
When I have it in bits I will try connecting the Ct direct..see what happens
I will post what I find..
Did you try the unequal resistors?
Background Hum etc is very low now..I will still try the direct connection..
Regards
M. Gregg
I am waiting for some coupling caps at the moment..
When I have it in bits I will try connecting the Ct direct..see what happens
I will post what I find..
Did you try the unequal resistors?
Background Hum etc is very low now..I will still try the direct connection..
Regards
M. Gregg
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Alastair,
I am going to have to try shorting out the 1K.. I have had comments by others that they had a big offset caused by this 1K with no load and also with full load.
This we have seen..
This is the question WHY did Tim Mellow put this in the PSU?
Thoughts are charge current and short fault causing major damage..
OK nothing in the cathode of the 6C33C's in other designs..
Well with the auto bias we do have a cathode resistor to limit fault current..
Possibily the cathode cap could blow,,,then again the fuse should go first..
So I see no gain in this 1K resistor...If the inrush is controlled.
So out comes the soldering iron....Shame I don't have the new coupling caps..
Curiosity has the better of me..
I will leave the other resistors as is for now..cathode current PI ect..
Regards
M. Gregg
I am going to have to try shorting out the 1K.. I have had comments by others that they had a big offset caused by this 1K with no load and also with full load.
This we have seen..
This is the question WHY did Tim Mellow put this in the PSU?
Thoughts are charge current and short fault causing major damage..
OK nothing in the cathode of the 6C33C's in other designs..
Well with the auto bias we do have a cathode resistor to limit fault current..
Possibily the cathode cap could blow,,,then again the fuse should go first..
So I see no gain in this 1K resistor...If the inrush is controlled.
So out comes the soldering iron....Shame I don't have the new coupling caps..
Curiosity has the better of me..
I will leave the other resistors as is for now..cathode current PI ect..
Regards
M. Gregg
Just for interest,
Again based upon tests done recently,
Also great help from members.
It seems that if the Ct is diconnected we lose bass response in this design..
This was confirmed by tests I have done and thoughts from members seem to point to, the cathode caps being in series with PSU caps lowering effective capacitance of the cathode bypass..hence lower bass..breathe..lol
So I know Ct must be connected (even with 1K is fine)..how much better it may be "direct" I will know soon..
However thoughts are still with speaker protection..If I used 500 Ohm will it be half as good..LMAO
Ah well..its times like this you have a magic wand and zap, test, zap put back..LOL
LOL just did the calcs if 6c33c was short with 220 ohm cathode resistor whats the volt drop across "wattage dissipated" 4 Ohms in series..
I think were OK with direct conected Ct..
Regards
M. Gregg
Again based upon tests done recently,
Also great help from members.
It seems that if the Ct is diconnected we lose bass response in this design..
This was confirmed by tests I have done and thoughts from members seem to point to, the cathode caps being in series with PSU caps lowering effective capacitance of the cathode bypass..hence lower bass..breathe..lol
So I know Ct must be connected (even with 1K is fine)..how much better it may be "direct" I will know soon..
However thoughts are still with speaker protection..If I used 500 Ohm will it be half as good..LMAO
Ah well..its times like this you have a magic wand and zap, test, zap put back..LOL
LOL just did the calcs if 6c33c was short with 220 ohm cathode resistor whats the volt drop across "wattage dissipated" 4 Ohms in series..
I think were OK with direct conected Ct..
Regards
M. Gregg
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I should imagine with most/all designs you would see a drop in bass without the CT connected...
This is due to the fact (In 'normal') designs you have no DC return from each rail, only an AC drain via the PSU caps, which then are both fully in series with the signal.
--The centre-point of the caps, is a pseudo-ground only if the CT isnt connected, and will not respond to DC and attenuate extremely Low freq..
The Tim-Mellow design (IMHO no offence intended) is flawed in a number of ways. I dont like it, however those that built it, like it....
With the CT connected, of course, the 22K and 10K become innefective as the CT now connected will keep the CT at 'O' volts, (all things being equal) and you'll still have the offset on O/P term caused by 7mA PI current.
This could be rectified by adding suitable sized resistor from the neg rail to the O/P terminal, to flow the same current as the PI....
While experimenting the other day, (To replace the 6C33 with 6C41C) I had a valve arc...
The supply fuse blew and there was no other damage.
I was trying to be 'clever' and not change the 50V transformer supplying heaters. I used a large diode to half-wave rectify to halve the power.
--It Didnt!
Cathodes became too hot causing the arc in one valve....
Surprisingly, There was no hum when running on half-wave heater rectification either, although it made a nasty noise when arcing....!
This is due to the fact (In 'normal') designs you have no DC return from each rail, only an AC drain via the PSU caps, which then are both fully in series with the signal.
--The centre-point of the caps, is a pseudo-ground only if the CT isnt connected, and will not respond to DC and attenuate extremely Low freq..
The Tim-Mellow design (IMHO no offence intended) is flawed in a number of ways. I dont like it, however those that built it, like it....
With the CT connected, of course, the 22K and 10K become innefective as the CT now connected will keep the CT at 'O' volts, (all things being equal) and you'll still have the offset on O/P term caused by 7mA PI current.
This could be rectified by adding suitable sized resistor from the neg rail to the O/P terminal, to flow the same current as the PI....
While experimenting the other day, (To replace the 6C33 with 6C41C) I had a valve arc...
The supply fuse blew and there was no other damage.
I was trying to be 'clever' and not change the 50V transformer supplying heaters. I used a large diode to half-wave rectify to halve the power.
--It Didnt!
Cathodes became too hot causing the arc in one valve....
Surprisingly, There was no hum when running on half-wave heater rectification either, although it made a nasty noise when arcing....!
Alastair,
That's great news..ok not for the tube..
I can't comment about other designs and bass Ct or effects first OTL I have experience with..However there is a bass reduction no question about it!
What size resistor you goin to put in the negative rail then?
Alastair,
Could you do some measurements for power out THD etc..and post if you get time!
I have had a few people ask..It seems some are interested..
Regards
M. Gregg
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Resistor from Neg rail to O/P term would need to be around 22K or a little higher.
We are only looking to flow approx 6 mA to compensate for the PI current which should be also around 6 mA
--This will then effectively form a sorta potential-divider with the PI and cancel out the offset caused by the current return from the PI into the O/P term.
Realistically though, you'll probably have a bigger offset from the O/P valves themselves, and in choosing their position to minimise offset, you would have taken into account this small (Almost Non ) issue....
Offset across a 8ohm resistor is the best check though, rather than the O/C value...
Any testing that I now currently do however, would be done with 6C41C so wouldnt have much bearing on the design as described in this thread.
Maybe if you have the equipment/software, you could find what your current set-up is giving....
Not sure when I'll be able to get to do this...
Apparently, There's some pretty good freebie software able to check things like frequency-response, distortion etc but the quality of the readings depends on soundcard performance.
My soundcard is pretty crap so any results wouldn't be very accurate!
We are only looking to flow approx 6 mA to compensate for the PI current which should be also around 6 mA
--This will then effectively form a sorta potential-divider with the PI and cancel out the offset caused by the current return from the PI into the O/P term.
Realistically though, you'll probably have a bigger offset from the O/P valves themselves, and in choosing their position to minimise offset, you would have taken into account this small (Almost Non ) issue....
Offset across a 8ohm resistor is the best check though, rather than the O/C value...
Any testing that I now currently do however, would be done with 6C41C so wouldnt have much bearing on the design as described in this thread.
Maybe if you have the equipment/software, you could find what your current set-up is giving....
Not sure when I'll be able to get to do this...
Apparently, There's some pretty good freebie software able to check things like frequency-response, distortion etc but the quality of the readings depends on soundcard performance.
My soundcard is pretty crap so any results wouldn't be very accurate!
Alastair,
Here is a suprise for me any way...
I have connected the Ct direct....and yes a slight reduction in noise...But..
The bass is less refined....It's early to tell yet..
I'm going to listen for a while but I think there will be a value going back in what thet will be I'm not sure yet!
I may try the my joking remark of 500 Ohms..
Regards
M. Gregg
Here is a suprise for me any way...
I have connected the Ct direct....and yes a slight reduction in noise...But..
The bass is less refined....It's early to tell yet..
I'm going to listen for a while but I think there will be a value going back in what thet will be I'm not sure yet!
I may try the my joking remark of 500 Ohms..
Regards
M. Gregg
Hmm....
'Less refined'
I wonder, if the phase-shifts that are probably happening at these lower frequencies caused by the PSU caps in series with the signal without the CT connected, are causing the bass differences that are a pleasing effect for you....
Or maybe I'm just talking crap!--Sound is just so subjective and so difficult to describe in words!
I would have thought without the CT connected, the bass would be 'wolly' or boomy/vague sounding, less defined....
'Less refined'
I wonder, if the phase-shifts that are probably happening at these lower frequencies caused by the PSU caps in series with the signal without the CT connected, are causing the bass differences that are a pleasing effect for you....
Or maybe I'm just talking crap!--Sound is just so subjective and so difficult to describe in words!
I would have thought without the CT connected, the bass would be 'wolly' or boomy/vague sounding, less defined....
Its hard to describe but here we go...there seems to be less bass and its grainey buy comparison.. not so smooth sounding..hard on the ear..
I don't know if this makes sense but its less musical..
The problem is this could be the components used etc..
I'm almost tempted to put a couple of flying leads and variable power resistor and try different settings,,to see what the effects are..
We know that there is an effect if its disconnected and put back...so I have to assume that I am hearing something..what that is I do not know..
Regards
M. Gregg
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