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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 345

post #5161 of 8421
Quote:
Originally Posted by gibosi View Post
 

Glad to hear that everything is working well for you. And yes, it is great to be able to kill two birds with one stone. Now we can roll higher heater current tubes, like 6SN7, E80CC and ECC40, and our amps are quieter! Win-win!! :)

 

I've got a new production Tung-Sol 6SN7GTB I'm listening to right now which also sounds really good based on a few minutes of listening.

post #5162 of 8421

Hi mab1376 et al,

 

Re the little voltage regulator, my impression is that the LED readout is stepped; i.e it goes from 6.27V to 6.43V to 6.52V in my case. However, you can turn the little set screw about a quarter of a turn or so without changing the LED readout value, but a multimeter will show the voltage changing in between these readings.

Therefore, I am able to adjust the voltage to exactly 6.3V using the multimeter with the LED readout still showing 6.19V or 6.27V etc.

 

My nature is such that I'd rather have it at 6.3V than be content with 6.19V or 6.42V.

 

Something else I discovered - the voltage can show 6.3V at the regulator output terminals, but read 6.19V at the socket on my breadboard. I have two setups using breadboards; one for 6/8FQ7 and 6DJ8 tubes, and another for 12AX7 and octal tubes (with an adapter). The first setup reads the same voltage at the socket pins as at the voltage regulator, but the second setup reads lower than at the regulator. In order to get 6.3V at the tube socket I need 6.52V at the regulator (don't know why).

 

I would recommend measuring the voltage at the tube socket just to be sure. I am doing this with everything turned on and a tube in place, being very careful only to touch the correct pin tabs with the test leads. As has been pointed out previously, some pins carry dangerously high voltage, and I mounted the regulator and breadboard on a piece of wood so that I can't touch anything underneath by accident.

post #5163 of 8421

Re the new Tung Sol tube vs an old one, have you been able to compare them?

 

From what I read the new production tubes are good, but most people seem to prefer the old ones.

 

I am coming in without any preconceived ideas, and I am just giving over my listening impressions as honestly as I can.  My goal is to try to find the inexpensive giant killers. So far I have not read much about the Japanese Raytheon 8FQ7 and RCA 6SN7GTB 1965-67 tubes with the thin heater wire above the top mica, but to me these tubes sound fabulous.

 

At this time these tubes can be found for less than $5.00 if you shop carefully. Would like to hear from others who tried these tubes.

post #5164 of 8421
Quote:
Originally Posted by mordy View Post
 

Re the new Tung Sol tube vs an old one, have you been able to compare them?

 

From what I read the new production tubes are good, but most people seem to prefer the old ones.

 

I am coming in without any preconceived ideas, and I am just giving over my listening impressions as honestly as I can.  My goal is to try to find the inexpensive giant killers. So far I have not read much about the Japanese Raytheon 8FQ7 and RCA 6SN7GTB 1965-67 tubes with the thin heater wire above the top mica, but to me these tubes sound fabulous.

 

At this time these tubes can be found for less than $5.00 if you shop carefully. Would like to hear from others who tried these tubes.

 

The new production sounds much brighter whereas the older ones sound sweet and more balanced. I very much like the new ones from the few minutes i have comparing them, I could easily recommend them as a cheap starter tube I also have a Sylvania 6SL7WGT from 1955 which sounds similar to the old Tung Sol but has a much larger sound stage to me.

 

This whole vast new world of tubes is already becoming overwhelming lol

post #5165 of 8421
Quote:
Originally Posted by mordy View Post

In order to get 6.3V at the tube socket I need 6.52V at the regulator (don't know why).

 

That is very strange mordy,

 

Are you still using solid core wire to connect everything? It really sounds to me like there is a resistor in series with the heater wiring. The short distance the wire travels from your power board to your breakout board would have a very minute effect on the voltage, but you are almost loosing 1/2 a volt.

 

If you want to try something take a piece of Lamp Cord (Zip Cord we call it) or something similar and use it to wire up your filaments.

Then check your voltage at both ends and see if there is any drop. If there is a difference unhook the wires connected to the breakout board's filament pins and measure the voltage at the end of the unconnected wire. (Keep your amp powered off for that test.)

:beerchug: 


Edited by TrollDragon - 2/27/14 at 8:41pm
post #5166 of 8421

How difficult would it be to put a switch on the output of the regulator to turn it on and off?

post #5167 of 8421

Yesterday, received an ECC40, manufactured in February, 1952. However I am not at all sure about the factory. The production code appears to be LCC 5S, and if the first character in the second picture is actually a "5", this would indicate Toshiba, Japan. But if so, this would imply that Philips production equipment was installed into a Japanese factory by 1952 and that factory was using Philips production codes. Silk-screening on the tube indicates Holland manufacture, but we know from past experience that we can't necessary believe this. I do not know what to think....

 

However, regardless of where this tube was manufactured, it sounds great! :)

 

 

post #5168 of 8421
Quote:
Originally Posted by gibosi View Post
 

Yesterday, received an ECC40, manufactured in February, 1952. However I am not at all sure about the factory. The production code appears to be LCC 5S, and if the first character in the second picture is actually a "5", this would indicate Toshiba, Japan. But if so, this would imply that Philips production equipment was installed into a Japanese factory by 1952 and that factory was using Philips production codes. Silk-screening on the tube indicates Holland manufacture, but we know from past experience that we can't necessary believe this. I do not know what to think....

 

I think the code was originally used by some Philips department in Eindhoven, later for Toshiba-made tubes.

post #5169 of 8421

I just picked up a smoked glass RCA 12SN7, the 6SN7 version goes for about $40 on ebay and i got the 12v version for $5 :)

 

Yay for mods!

post #5170 of 8421
Quote:
Originally Posted by Oskari View Post
 

 

I think the code was originally used by some Philips department in Eindhoven, later for Toshiba-made tubes.

 

Thanks! Eindhoven certainly seems to make more sense than Toshiba for this tube.

post #5171 of 8421
Quote:
Originally Posted by mab1376 View Post
 

I just picked up a smoked glass RCA 12SN7, the 6SN7 version goes for about $40 on ebay and i got the 12v version for $5 :)

 

Yay for mods!


Please excuse my naivety but I have to ask a potentialt silly question. To use a 12sn7 with a custom Octal adapter with external step-down power supply on a LD MKiii, is it as simple as turning up the power supply to 12volts?

post #5172 of 8421
Quote:
Originally Posted by samtheman View Post
 


Please excuse my naivety but I have to ask a potentialt silly question. To use a 12sn7 with a custom Octal adapter with external step-down power supply on a LD MKiii, is it as simple as turning up the power supply to 12volts?

 

yup just increase the pot on the trimmer board to 12v output, as long as your PSU supports 12v at 600ma that's the only thing you need to do.

 

I'm currently using the power adapter from a Nintendo Wii that i recently threw out since it was broken. I'd like to find something with an on/off switch though.

post #5173 of 8421
Quote:
Originally Posted by mab1376 View Post
 

 

yup just increase the pot on the trimmer board to 12v output, as long as your PSU supports 12v at 600ma that's the only thing you need to do.

 

I'm currently using the power adapter from a Nintendo Wii that i recently threw out since it was broken. I'd like to find something with an on/off switch though.

 

An on/off switch would be great. But in the meantime, I simply plug the LD and the adapter into a separate surge protector power bar and use that to turn both on and off. In this way, I don't have to worry about inadvertently leaving the heaters on when I turn the LD off.

 

Oh, while 6SN7s require 600ma, if you double the voltage to 12.6V, the amperage requirement drops by half to 300ma. :)


Edited by gibosi - 2/28/14 at 8:43am
post #5174 of 8421

That's good to hear - just waiting on my Step-down converter to arrive in the post. The wait is making me crazy. Everything else for the adapter is built.

 

I have just dug-up another power adapter with an output rated as 6v at 600ma. Would this do the job for 6SN7 tubes while I wait for the converter? Does 6volts vs 6.3 volts make a big difference?

post #5175 of 8421

Hi samtheman,

 

6V won't do the trick. The voltage regulator works in such a way that what comes out is around 2V lower than what goes in. In order to get 6V out you need at least an 8V adapter. To be able to use the voltage regulator for a variety of tubes from 6V - 12V it is best to get an adapter capable of at least 15V.

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