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Old 28th October 2012, 06:03 AM   #1151
tubo is offline tubo  Philippines
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Quote:
Originally Posted by Tony View Post
i do not think so, look at the heater cathode voltage ratng, they should be about 300volt or so...http://tubedata.milbert.com/sheets/093/6/6AX4GTB.pdf

do not put too much faith on "rectifier tubes singing", their mission in the amp is to convert ac to dc and not have too much forward drop....
Hi tony,

Thanks for the input. Yea I got the 6ax4s for less than a dollar a pop. Actually I got them at a garage sale along with a single altec 605a for $10 bucks.
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Old 28th October 2012, 11:28 AM   #1152
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AC voltage on the heaters for the 6v6 was inho the way to go. I tried various DC set-ups including a SSLVR and all of them sounded dead to me. So I am back to a simple tranny and a resistor to keep the voltage down to 6.1V. It is a matter of opinion though.
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Old 28th October 2012, 11:47 AM   #1153
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same experience here...i do lift the heaters to dc though....
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Old 28th October 2012, 11:52 AM   #1154
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Yep I do as well. Lift about 20Vdc presently.
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Old 28th October 2012, 11:57 AM   #1155
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Could you show a schematic. This is basically tying ground of the heater to a higher voltage tapped off mains supply? Are you using SSHV2, SGrergory?
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Old 28th October 2012, 12:31 PM   #1156
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Yes I use the SSHV2.
FYI, I also use a ccs as the load. I built the Bootstrap CF.

To lift the heater it is a simple, a relativly high impedance voltage divider. If you know your B+ voltage then calculate the value of the divider to get the proper voltage. You will also need to bypass the lower resistor to ground with caps. I used a 1uF poly and a 47uF electrolytic 50V I had out of my parts box. I will see if I can draw a quick schematic later and post if someone doesn't have it handy. Pretty common approach
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Old 28th October 2012, 12:42 PM   #1157
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THanks. First time I will have done it, so just being careful.
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Old 28th October 2012, 01:33 PM   #1158
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Default Voltage divider for lifting heaters

Here is what I use for lifting heaters. Lots of opinion and theories as to what voltage to lift heater to. I try to keep it simple.

For me: Rule number one. Make sure that the heater to cathode voltage is within spec. Then, if feasible, select a voltage to get the heater above the operating cathode voltage slightly.
Attached Images
File Type: jpg Voltage Divider003.jpg (317.7 KB, 262 views)
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Old 28th October 2012, 02:02 PM   #1159
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Just to be sure. V1 is the point where your heater circuit would normally tap ground.
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Old 28th October 2012, 02:11 PM   #1160
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Yes. V1 is the "new ground" for the heater circuit. I just tie one leg of the heater trany out to it. In my case I rarely use the PT heater windings and opt for a seperate heater tranny. But this works in any case.

Attached photo is of complete heater supply including voltage drop resistors for 6.1V and Voltage divider for lift. You can see the caps and smaller resistors buried underneath Vdrop resistors
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File Type: jpg 6v6 heater supply web.jpg (30.8 KB, 238 views)
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Last edited by SGregory; 28th October 2012 at 02:19 PM. Reason: added photo
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