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Old 10th February 2012, 04:38 PM   #41
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Hi,

Already have high melting point solder ready and waiting.

I have burned output tubes for 5 hours each heaters only, I will then run up amp for a couple of hours with bias pot at minimum (hopefully 100ma or so).

Only have 4 of these tubes so not a lot of choice with pairing.

Hi precision resistors are by Welwyn.

Progress today.. LHC driver wiring completed, doing the other channel should be a lot quicker now I have worked out the layout.
n.b. tagstrip at back goes straight to the triodes of 6c33s... so not a lot more to do just routing of PSU rails and connection to bias pot centre
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Old 10th February 2012, 05:07 PM   #42
djn is offline djn  United States
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Hi Smith, are you building straight from Tim's original scheem? I just found enough copper plate to make both my chassis and want to start this build as soon as I finish two others. I am looking for 2 meters for this and would like them to be old style round no bigger than 2 inches across. Any idea where I might find them? D.
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Old 11th February 2012, 07:11 AM   #43
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Hi, D
I am working from Tims article published in Audio Xpress magazine 2/10

(N.B. the March 2012 edition is now available on-line.... just Google it.)

The only changes that I have made are to up rate C18 to 500v (as it must have at least 280v across it) plus I am using 500ma meters and I have only included one fuse, the one in the +150 supply.
Apart from my choice of input and coupling capacitors the circuit and the rest of the components are as per Tims spec.

Please can you explain what you are looking for I don,t understand what you mean "old style round 2 inches across" ?
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Old 11th February 2012, 08:46 AM   #44
M Gregg is offline M Gregg  United Kingdom
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Quote:
Originally Posted by smith01793 View Post
Hi,

Already have high melting point solder ready and waiting.

I have burned output tubes for 5 hours each heaters only, I will then run up amp for a couple of hours with bias pot at minimum (hopefully 100ma or so).

Only have 4 of these tubes so not a lot of choice with pairing.

Hi precision resistors are by Welwyn.

Progress today.. LHC driver wiring completed, doing the other channel should be a lot quicker now I have worked out the layout.
n.b. tagstrip at back goes straight to the triodes of 6c33s... so not a lot more to do just routing of PSU rails and connection to bias pot centre
You know,

I don't think 5 Hrs with heater will cut it..you may get away with it, I was told not less than 12hrs ie a whole day heaters only no bias..(this was supposed to be taking a risk)
Then let them cool and give it another couple of hours..before any B+ or low bias..

If it hasen't been enough they will flash over and their history..

The tubes are supposed to expand during this time and settle into a running position.

Regards
M. Gregg
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Last edited by M Gregg; 11th February 2012 at 08:51 AM.
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Old 11th February 2012, 09:57 AM   #45
M Gregg is offline M Gregg  United Kingdom
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Quote:
Originally Posted by smith01793 View Post
Hi, D
I am working from Tims article published in Audio Xpress magazine 2/10

(N.B. the March 2012 edition is now available on-line.... just Google it.)

The only changes that I have made are to up rate C18 to 500v (as it must have at least 280v across it) plus I am using 500ma meters and I have only included one fuse, the one in the +150 supply.
Apart from my choice of input and coupling capacitors the circuit and the rest of the components are as per Tims spec.

Please can you explain what you are looking for I don,t understand what you mean "old style round 2 inches across" ?
Just a quick question,

Only one fuse in the +150?
I thought that the CT of the Tx would give you a short through the bottom tube if it goes short? and stuff the speaker?

Regards
M. Gregg
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Old 11th February 2012, 05:31 PM   #46
djn is offline djn  United States
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Thanks Smith. I am making the two chassis out of copper and would like to find old brass round meters. Just to complete the look.

Quote:
Originally Posted by smith01793 View Post
Hi, D
I am working from Tims article published in Audio Xpress magazine 2/10

(N.B. the March 2012 edition is now available on-line.... just Google it.)

The only changes that I have made are to up rate C18 to 500v (as it must have at least 280v across it) plus I am using 500ma meters and I have only included one fuse, the one in the +150 supply.
Apart from my choice of input and coupling capacitors the circuit and the rest of the components are as per Tims spec.

Please can you explain what you are looking for I don,t understand what you mean "old style round 2 inches across" ?
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Old 11th February 2012, 06:06 PM   #47
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Hi, M Gregg

Thanks for the feedback I will burn the 6c33's for a few more hours each.

In Tims design the the centre tap is connected through a 1k resistor for stabilisation purposes only. if the + 150v fuse fails all the voltages will drop as this this is the top feed to a capacitive divider, the -150 rail is effectively the "ground" point so
it should be O.K. with one fuse.
The following is copied from the article by Tim ;-

"Fuses F1 and F2 are provided in the unlikely event that both driver tubes, V2
and V3, fail (or not being plugged in),thus causing an excessive current to flow
through both output tubes V4 and V5. In theory, only one fuse is needed, but
two are included here in order that any non linearity they produce is symmetrical"

On my panel layout I have allowed for one fuse in the middle, I have a good ear, but I cant hear the difference that a fuse makes to a circuit.

Tony.
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Old 11th February 2012, 06:10 PM   #48
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Djn,

Have you considered using standard round Bakelite meters?
you could paint them with conductive paint and then electroplate them using a brush plating kit, Available on ebay.
Tony.
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Old 11th February 2012, 06:47 PM   #49
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further to the whole fuse centre tap thing,

I forgot to mention previously that I am using a 500w mains isolation transformer with no centre tap, this has been done before.. one guy has built two of them,one for himself and then one for his son.

if stabilisation is a problem then 2 x 1k 15w resistors forming a potential divider across the transformer would have the same effect as Tims 1k to the CT.
The 30w dissipation would be a problem for most designs but I would not have an issue with this as they could be placed with the transformer and help to heat heat the rest of the room.

Tony.
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Old 11th February 2012, 06:56 PM   #50
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a picture of the Beast.
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