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Old 16th August 2005, 03:53 AM   #21
amperex is offline amperex  United States
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If the amp provides less than good sonics, the 811A best be kept to high voltage RF or modulator service. Radio Daze in NY sells the available 812 for $42 each. AES has the 812 available from China, Russia & NOS US manufacture. A heavy duty version was manufactured with a 572B type carbon plate called the 812H. Now, that is a rare tube.
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Old 16th August 2005, 01:20 PM   #22
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Default It lives !!!

I have constructed the amp last night it works with a 811 a 6v6 and a 6j7

one thing that i am concerned about is that the grid has 16+ on it do you think this is alright for an 811 ? i am running the anode on exactly 300 v the amp itself works great

thanks

MW3KGQ
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Old 16th August 2005, 05:59 PM   #23
jim is offline jim  Belgium
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Quote:
one thing that i am concerned about is that the grid has 16+ on it do you think this is alright for an 811 ? i am running the anode on exactly 300 v the amp itself works great
Should be ok
Have you measured the anode current.
Together with the grid voltage and anode voltage this will give you the working point.
Check it with the 811A data.

Greets,
Jim
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Old 17th August 2005, 08:07 AM   #24
CLS is online now CLS  Taiwan
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Default Re: It lives !!!

Quote:
Originally posted by john 807
I have constructed the amp last night it works with a 811 a 6v6 and a 6j7
...
Great! I'm very interested. I happen to have these tubes on hand.

Would you please share some more about how it sounds?

About the grid voltage, I believe, at +16V (with 300V on anode), it's just awakened.

I tried marking that point on the plate curves, I saw only around 40mA. It's indeed in the far left/bottom region of the chart.

On Shishido's design, it runs the tube at 440V / +30V / 100mA with 3.5k load. FYR
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Old 17th August 2005, 05:37 PM   #25
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Default I am Glad you have taken an interest

HI

Well, I am only 14 but I had the valve in my collection and I had a output transformer needs to be within the region of 3.5 to 5k at about 15watts rated the 811-A runs about +300v on the plate witch is cathode driven you can use some of the circuits on this thread. it draws the minimiun of about 100ma
that some kind people have offered to share with us. it is driven using the 6V6G and as a pre gain stage you will need a 6j7 or some over kind of pentode of your choice i used the 6J7 because it looks cool next to the 811 coke-bottle style but you
can use any style of pentode to use as the pre amp there is not a circuit for that i made it up if you need help with it i will give you them in a seperate thread

Warning - High voltages are present !!!

And you can have problems with the hum i didnt cause i used a big meaty capacitor (22000 uf +22000 uf 62v dc wrk) with a 2mh choke needs to be heavy or it will over heat as i had problems with i used a battery chager transformer for the heater and it worked very well gets warm

experements - it works very well the bass is so well held the high freq 's need to be held down with a bit of negitive feedback
NFB but overall a very good reasult

this amp is certanly one of the most fun to experement with a used my transmitter power supply to run the 811 on about 800+v
made the valve work a bit harder for a few more watts but that was only for experement i run it only on about 300 The rectifire is a GZ34 it gives the best voltage boost A 5U4 saggs the B+ down a lot a coventional choke needs to be used for HT smmothing at a bout 10H minimium

I will get some pics soon!!!

Jonathan Kelly
MW3KGQ
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Old 18th August 2005, 12:27 AM   #26
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Default BIAS

HI All

sorry the last one was quick has a few mistakes in it,
anyway the bias improves the sound quality a lot and power
output ( PD ) it is worth checking the data sheets and reading the graphs to understand the bias points to run the 811-a at you can do it very easily by ploting your H.T Volts by your H.T Current and you get a result I will test it tommrow seen as it will wake every-one up and i will be popular

73,s

MW3KGQ
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Old 18th August 2005, 05:41 AM   #27
CLS is online now CLS  Taiwan
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Good for you, Jonathan !
How I wish I could be like you in my youth.


Back to the circuit, I supposed there're both driver's Ia + 811's Ia on the Rk of 811.

So if you measured the voltage across the Rk of 811, you couldn't see the Ia of 811 alone, and there's also grid current in it.

Correct me if I'm wrong.
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Old 18th August 2005, 11:09 PM   #28
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Default Right you are

Yes,
you get the reading of the bias of the driver valve which is controleing the 811 so the bias is infact controlled by the driver in my case 6v6 I must admit i have a problem with it i am getting something called ( cross-over-distortion ) and not enough out-put
(PD) it is becomeing difficult to sort my dad is having a think about it should be resolved.

Grid curent - nope thers no current draw it is voltage swing the circuit is very strange to most valve-amp-constructors because it uses + bias the idea of using such a powerfull driver is so that it can swing the volaage 80+ and back down to 80- again you need a very big valve to do this with triodes it is the same with the 300b and other valves alike. the 6v6 can give 5w to 10w depending on the plate voltage. now this is a usefull trick I am going to tell you if you havent enough b+ to drive the 6v6 to maximum output you can use a 6Y6 or an other one in the family is the 6F6 saves a lot of time and confussion they can be pluged into the same pin connections as well also if your after a bit more power you can use the 6L6 best of building the amp around the 6v6 and then experement later

so , are you going to give it ago ???

I am very tired today after last night tinkering to one in the morning so i haven't done much with it i hate it when i am tired it really annoys me

Best wishes

Jonathan kelly
MW3KGQ
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Old 18th August 2005, 11:14 PM   #29
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Default mistake!!!

There is grid current sorry !! because the 811 is drawing it of the 6v6 as it is driving it as well as the voltage swing to drive the valve within it class of drive except it is + not- drive

Jonathan
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Old 19th August 2005, 02:24 AM   #30
CLS is online now CLS  Taiwan
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How about installing a 'grid stopper' for 811?

A small one like 10R~100R would be sufficient I guess. With this resistor in place, you can monitor the actual current through 6V6. (and that is also the grid current of 811)


PS. I'll build such an amp for sure, but it takes time. For a 'middleager' like me, free time is the most luxurious thing.
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