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Old 6th January 2012, 07:48 AM   #721
M Gregg is offline M Gregg  United Kingdom
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Quote:
Originally Posted by Alastair E View Post
Worth remembering the Impedance presented to the amp by the speaker at or near its freq of resonance, --for the Alpair 7 70 Hz, its many times the DC or quoted nominal impedance...

For the Alpair, its approaching something like 50 ohms at 70 Hz, therefore an easier load for the amp and more effective power can be realised.....
The only trouble is..

When you power them for the first time you can only have them at transistor radio volumes (I have a feeling you would damage them if you try to push them their so tight) and they produce what sounds like "0" bass...Then a very slow break in period over 6 Months..LOL

Then your stuffing polyfluff in the vent to reduce the bass...cuz its so loud..LOL

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M. Gregg
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Old 17th January 2012, 09:42 AM   #722
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Yes i see it

Thanks
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Old 28th January 2012, 02:47 PM   #723
M Gregg is offline M Gregg  United Kingdom
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OK just an update,

The toroids now have cork pads under the rubber pads made from cork tiles..
Result reduced Tx noise (mechanical)..
(Tx under rated no heat issue)

The 0.22 interstage cap was changed just for a laugh to Obbligato 630V <<(seem to like violin don't know why)
I would never have tried them except I was interested in price Vs performance...Compared to jupiter HT in this part of this circuit..Well yes different..for the price you have got to try these

Switched on Jessie J and goose bumps..LOL


So as it stands now for a laugh orange drop to Op tubes and as above..LOL

The saga continues...

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M. Gregg
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Old 28th January 2012, 03:08 PM   #724
M Gregg is offline M Gregg  United Kingdom
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Just a thought

Orange drop are 716 not 715<<<there is a big difference!


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M. Gregg
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Old 28th January 2012, 04:57 PM   #725
M Gregg is offline M Gregg  United Kingdom
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Error,,

Post #723

LOL I thought I better say knowing how pedantic the forum can be,

I mean the Power Tx's are over rated not under rated for the job..


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M. Gregg
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Old 30th January 2012, 04:58 PM   #726
M Gregg is offline M Gregg  United Kingdom
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Alastair,

You are correct with the nipple distortion..I have found that a low value of resistor on the grid of the PI is an issue. I now have 120K in this postion.

The effect sounds like the speakers are out of sink with each other..a bit like some else is singing along very quietly...quite a strange effect..

This also gives reduced power available due to the overriding distortion effecting the OP at higher powers.. So your right again...LOL

Just for fun the 1813 vishay caps (output to 6C33C) give a tighter base with the Obbligatos in the interstage position..may not be of interest..

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M. Gregg
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Old 31st January 2012, 11:52 AM   #727
M Gregg is offline M Gregg  United Kingdom
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Final comment on the caps,

All now as in post #723,

0.47uF 400V 716 orange drop OP to 6C33C and 0.22uF 630V Obbligato gold in the interstage cap position. (Works well with most sources)..
Cheap and works very well...(good low level detail)

With the change of PI grid resistor (metal film) is 120K..

No comments on the high end stuff..each to his own...

I guess its time to look at other things..LOL

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M. Gregg
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Old 31st January 2012, 04:31 PM   #728
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Sounds like you been having lots of fun!

Yes--That resistor helps with distortion at the high signal-levels, to help even more, a greater supply volts to the PI would be good, so the 'headroom' before clip/dist would be higher...

A different valve for the PI would be another option....
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Old 31st January 2012, 08:13 PM   #729
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Quote:
Originally Posted by M Gregg View Post
OK just an update,

The toroids now have cork pads under the rubber pads made from cork tiles..
Result reduced Tx noise (mechanical)..
(Tx under rated no heat issue)

The 0.22 interstage cap was changed just for a laugh to Obbligato 630V <<(seem to like violin don't know why)
I would never have tried them except I was interested in price Vs performance...Compared to jupiter HT in this part of this circuit..Well yes different..for the price you have got to try these

Switched on Jessie J and goose bumps..LOL


So as it stands now for a laugh orange drop to Op tubes and as above..LOL

The saga continues...

Regards
M. Gregg
Its good to play with different type of capacitors , but not overdo it , it will became "cheaty" , there is still many experiments to do , to "improve " the sound of thge amp .
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Old 1st February 2012, 12:05 PM   #730
M Gregg is offline M Gregg  United Kingdom
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I think,

If I was going to mod then in order of preference they would be:

Increase the B+ on the PI to 500V

Use Fet driver direct onto 6C33C tube grid

Change PI to 6V6 or 6L6

Taking in to account that the amp is built then these are questionable..

But...

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M. Gregg
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