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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 281

post #4201 of 10780
Quote:
Originally Posted by gibosi View Post
 

 

Thank you for making sure I don't break my LD! :)

 

However, as I still have plenty of tubes to roll that are perfectly safe to run in the LD, I think I will file this idea away until the time comes that my itch to run these higher current tubes becomes intolerable! lol

 

Thanks again! :) 

 

The urge will come...

 

I mean, look at all of us on this thread lol! No one has ever resisted an urge yet.

 

And yeah, I'm itching to try a 6N30P in the driver position myself....

post #4202 of 10780

Was checking code on Orange Globe tube and i noticed that behind where its written made in Holland theres this  GAC and below 47k2 and other tube is GAB and 47A5 is that a date anybody know these codes. Thanks

post #4203 of 10780
Quote:
Originally Posted by MIKELAP View Post
 

Was checking code on Orange Globe tube and i noticed that behind where its written made in Holland theres this  GAC and below 47k2 and other tube is GAB and 47A5 is that a date anybody know these codes. Thanks

GA = 6DJ8 / ECC88

 

C and B are change codes. The earliest change codes were represented with numbers, and after the number 9, letters. You might consider this a "version number" So one tube is version B and the other is version C.

 

4 = Heerlen, Holland. It is actually a triangle on its side, many refer to this character as a "delta"

7 = 1967

A - L = Month... so A = January and K = November

1 - 5 = week of the month.

 

So both tubes were manufactured in the Heerlen, Holland factory in 1967, one in January and one in November.

post #4204 of 10780
Quote:
Originally Posted by gibosi View Post
 

 

Would you be willing to provide a primer on how to make these measurements? My system, with a breadboard 9-pin socket and 7-pin Vectors, certainly provides full access. However, I have no good idea how to make these measurements.

 

Also, in case it makes a difference, I have an LD 1+, which is a hybrid amp, and it is my understanding that the tube stage is configured as a cathode follower.....

 

Are these AC Volt measurements? or the DC?

 

If I put the one of the meter's probes on Vector pin 3, one of the heater pins, where do I put the other probe? Pin 4? Somewhere else?

 

In the same vein, if I put one of the meter's probes on Vector pin 5, the plate, where do I put the other probe?

 

And the same question for the grid?

 

Further, is there anything else you think a rank amateur should know?

 

Thank you!

 

Heater Voltage - Set your meter to Volts AC , put one probe on pin 3 , the other on pin 4.

Plate Voltage - Set your meter to Volts DC , put the red probe on pin 5, the black probe to Ground. On the MK111 the best place for ground is the case screw next to the right hand driver tube. Not sure about the LD 1+ but a convenient place on the case should be fine.

Grid Voltage - Set your meter on Volts DC , put the red probe on pin 2 , the black probe to Ground. This is actually measuring the cathode bias voltage but at idle the grid is 0 volts so this amounts to the same thing.

 

Be very careful when taking measurements not to short out adjacent pins and normal disclaimers of at your own risk applies of course.

 

The output stage of the LD 1+ is different as you say, so I don't know what effect a plate voltage greatly different from the norm will have on the sound.

post #4205 of 10780
Quote:
Originally Posted by Ctritical Bill View Post
 

Be very careful when taking measurements not to short out adjacent pins and normal disclaimers of at your own risk applies of course.

 

Thank you! I will try to take some measurements on a few E88CC and E188CC  over the next day or two and post them. Cheers. :)

post #4206 of 10780
Quote:
Originally Posted by Audiofanboy View Post
 

The urge will come...

 

lol...yes I am sure it will come! 

 

And it seems to me that when I get an external transformer to power the heaters, I may as well get one with a 12.6 volt tap as well. I assume that there might be some nice 12.6 volt double triodes we haven't been able to try yet? :)

post #4207 of 10780

This morning, measured a 1967 La Radiotechnique E88CC running in an LD 1+:

 

Heater  -  6.7v
Plate (R) - 84.6    Grid (R) - 2.90
Plate (L)  - 84.6    Grid (L)  - 2.86

post #4208 of 10780
Quote:
Originally Posted by gibosi View Post
 

This morning, measured a 1967 La Radiotechnique E88CC running in an LD 1+:

 

Heater  -  6.7v
Plate (R) - 84.6    Grid (R) - 2.90
Plate (L)  - 84.6    Grid (L)  - 2.86

 

Well, these look like pretty good values to me; it just goes towards confirming that the 6DJ8 types are well suited for the amp.

 

That heater value doesn't seem so good though... It's beyond the +/- 5% acceptable range. While it's probably not dramatic, it may very well be high enough to shorten the tube's life over time. Staying within 6.3V +5% would be better - a value lower than 6.3V -5% might just make tube not sound as good but not damage it.

 

After reading the comments here about how a higher filament current draw seems to lower the filament tension somewhat, I'm thinking that's yet another reason to just use two separate double triodes - despite it being wasteful of tubes and power. I'm wondering if going below 300 mA of current could be "bad" if it doesn't create enough of the "load" to have filament tension within specs. At least, a 6DJ8 (365 mA) or a 7308/E188CC (335 mA) stays closer to the current draw two 6AK5 tubes (2 x 175 mA = 350 mA) would have; a 6922/E88CC actually goes below that.

 

Curious as to how the readings would turn out on a MK III or IV now. It was definitely a good call to start getting measurements, if only to err on the side of caution...

post #4209 of 10780

Hi Ctritical Bill,

 

If I understand correctly, the measurements you list are for 6DJ8 tubes. Would taking measurements for 12AX7 and octal tubes use different pins?

 

If i had the tube on a breadboard, can I measure voltages at the breadboard connectors? (Seems safer)

post #4210 of 10780

Finally! A Dario-branded, Heerlen, Holland-made E188CC, VR2 40H3, arrived in today's mail from France. After a quick inspection, it appears to have the same construction as the US-made Amperex 7308, as one would expect.

 

When I took the package out of the mailbox, I noticed that something was rattling around inside the box. Sure enough, the tube had slipped out of the bubble wrap and as the packing material was very sparse, the naked tube was rolling around in the box. (>_<) However, plugged it in, fired it up and all seems well. One very tough tube it seems... burning in as I write this....

 

post #4211 of 10780

Now for the 12v. adaptor, if i remember correctly the 6su7 octal works both with 6v. and 12 v. am i wright ,and now for the 12ax7 tubes dont have any of those i wread the thread a bit and found the 5751 triple mica to be a good tube would anybody have any ideas regarding good 12ax7 tubes brand and style or are the 6DJ8 just better overall than the 12ax7 and they are not worth getting into. Thanks

post #4212 of 10780

Hi Mikelap,

 

Tried several 12AX7 tubes - the only one I really like is an early 1960s Sylvania that sounds very good. In general, it could be that the 6DJ8 family of tubes sounds better on the LD amps.

 

Now I have this single 1940-50s  octal National Union 6SL7 which is getting better and better. After about 100 (!) hours of burn in the bass is getting more and more distinct and powerful and the detail, imaging and sound stage all have improved. An absolutely delicious tube!

post #4213 of 10780

Very nice post, thanks for all the hard work!

post #4214 of 10780
Quote:
Originally Posted by mordy View Post
 

Hi Ctritical Bill,

 

If I understand correctly, the measurements you list are for 6DJ8 tubes. Would taking measurements for 12AX7 and octal tubes use different pins?

 

If i had the tube on a breadboard, can I measure voltages at the breadboard connectors? (Seems safer)

 

The instructions I gave were for the pins of a socket 7 tube. The principle is the same for any tube you just have to identify what each pin is connected to. The best place to take measurements is the most convenient to your setup so the breadboard connections would probably be best.

post #4215 of 10780
Quote:
Originally Posted by Audiofanboy View Post
 

Well, these look like pretty good values to me; it just goes towards confirming that the 6DJ8 types are well suited for the amp.

 

That heater value doesn't seem so good though... It's beyond the +/- 5% acceptable range. While it's probably not dramatic, it may very well be high enough to shorten the tube's life over time. Staying within 6.3V +5% would be better - a value lower than 6.3V -5% might just make tube not sound as good but not damage it.

 

Yes, 6.7v would seem to be a bit high, but if I understand things correctly, this is a function of the mains and the LD transformer, not the tube. I live in 120volt land and I measure 122v at the wall. Again, if I understand correctly, the transformer simply converts this to 6.7v. Perhaps if my mains was closer to 115VAC, the heater voltage would be correspondingly lower?

 

A 1960 Heerlen, Holland E188CC running in an LD 1+:
 
Heater  -  6.7v
Plate (R) - 81.5    Grid (R) - 3.1
Plate (L)  - 81.5    Grid (L)  - 3.1

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