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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 280

post #4186 of 10506
The problem with the filament windings is I really don't know if it would be safe to draw the whole 1A through one side or not. It all depends on the AWG of the wire used in the windings. If they designed this transformer so that each side only provided 500mA then drawing more than that would overheat the winding and one of the wires would burn open.

This transformer is custom made for LD so I am not sure if they would sell you a replacement or not, I have searched for a compatible replacement but I could not find any, it would have to be a custom wind, or you would have to find something that would fit the case and then modifications to all the heater connections would have to be done.

If you wanted to try high filament current tubes you can just roll the dice and hope you don't burn out your transformer or parallel the drivers heater wires together but that would require a scope to make sure the phase is correct. Pin 3&4 on all the different amps might not be hooked up the same way as there is no distinct markings on the wires.

Pick up a Crack or a Darkvoice as they would be some much easier to play with octals IMHO.
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post #4187 of 10506
Quote:
Originally Posted by TrollDragon View Post

You don't have the jumper in EF92 mode with the 6AH6 and a 2-7 jumper as well do you? That would short the plate, grid and cathode all together.

6AH6's need to be run in EF95 mode with a 2-7 jumper, that is the only way they work.

Check the table on page 77 for settings.
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Well I have used that chart as an reference when shopping for tubes. It actually has the tubes I mentioned in a nice row. I've ran them all in EF95 with the 2-7 wire with 0.33 success rate.

post #4188 of 10506
Quote:
Originally Posted by Kestovitutus View Post

Well I have used that chart as an reference when shopping for tubes. It actually has the tubes I mentioned in a nice row. I've ran them all in EF95 with the 2-7 wire with 0.33 success rate.

I have a very vague recollection that the Russian 6AH6 equivalents were slightly different tubes, that weren't without issues... You may want to try and grab a datasheet for those exact tubes on google to check whether they can be 2-7 strapped like the regular 6AH6.
post #4189 of 10506

anyone tried any of the French 6AM6S / 6064 by Thomson / CSF / Minatron? They look very nice tubes.

post #4190 of 10506
Quote:
Originally Posted by Nic Rhodes View Post

anyone tried any of the French 6AM6S / 6064 by Thomson / CSF / Minatron? They look very nice tubes.

I wouldn't bother with these... My limited experience with similar Thomson CSF tubes was pretty mixed (very microphonic and weak glass).

If you want nice EF91 tubes - the best actually - try the GEC CV4014.
post #4191 of 10506

I have shed loads of GECs EF91s and know them well but am more interested in finding out about these French tubes. They are beautifully made items (certainly not weak glass, quite the opposite), well presented smart looking, I was wondering if anyone had tried them.


Edited by Nic Rhodes - 12/3/13 at 11:54am
post #4192 of 10506
Quote:
Originally Posted by TrollDragon View Post

The problem with the filament windings is I really don't know if it would be safe to draw the whole 1A through one side or not. It all depends on the AWG of the wire used in the windings. If they designed this transformer so that each side only provided 500mA then drawing more than that would overheat the winding and one of the wires would burn open.

This transformer is custom made for LD so I am not sure if they would sell you a replacement or not, I have searched for a compatible replacement but I could not find any, it would have to be a custom wind, or you would have to find something that would fit the case and then modifications to all the heater connections would have to be done.

If you wanted to try high filament current tubes you can just roll the dice and hope you don't burn out your transformer or parallel the drivers heater wires together but that would require a scope to make sure the phase is correct. Pin 3&4 on all the different amps might not be hooked up the same way as there is no distinct markings on the wires.

Pick up a Crack or a Darkvoice as they would be some much easier to play with octals IMHO.
beerchug.gif

 

This is a very valid point that you bring up about the transformer.

We just don't know whether there are separate windings for each driver tube or not.

I found this interesting page on heaters : http://www.valvewizard.co.uk/heater.html and this part seems relevant : "Transformer centre tap: The traditional way to reduce hum is to use a heater supply with a centre tap and connect it to ground." That would appear to be what we have in the LD. And if LD went to the trouble of getting a custom transformer made which included a centre-tapped heater winding, then perhaps they ran separate wires to each tube (thus reducing current in each wire) also to reduce hum. The fact that there are separate pairs of wires to each tube is the perplexing part but if they were separate windings I would imagine the transformer would label them as such.

I ran my amp for an hour and a half last night and the body didn't get any hotter than usual although I didn't feel the temperature of the transformer cover. Also I think I might expect a bigger voltage drop if the 600ma tube was working from a 500ma supply.

 

I guess we just can't say for sure how the heater supply is connected so everyone should be aware there might be a problem using tubes requiring filament currents higher than 500ma.

post #4193 of 10506
Quote:
Originally Posted by mordy View Post
 

Based on the following, perhaps we can place this tube in the 40's:

 

Either that or 50s. I can't say which one.

post #4194 of 10506

Either that or 50s.

 

I have this notion that older tubes were better made, but perhaps it is tied to certain brands that became lower in quality as time went on. In any case, these old NU tubes keep on improving with use - now up to around 75 hours. Sound stage, sizzling cymbals, sweet mid range, slam ... I'm running out of esses sssss

 

What is so interesting is that we now have tubes that sound excellent in the LD, and it becomes a case of personal preferences what you like rather than picking the tube that has the least shortcomings.

 

However, every time I think that we have reached the summit, something new and better turns up!

post #4195 of 10506
Quote:
Originally Posted by Nic Rhodes View Post
 

I have shed loads of GECs EF91s and know them well but am more interested in finding out about these French tubes. They are beautifully made items (certainly not weak glass, quite the opposite), well presented smart looking, I was wondering if anyone had tried them.

 

In the first 10-15 pages of this thread someone (don de luca or don luca or whatever) tried supposedly French 6AM6S tubes, so you may be able to find impressions there. Not that I would even bother with EF91 anymore considering everything else out there, but that's just me ;) , those tubes are still interesting in their own right (and happen to kick the amp's ass with high mu and high gm; these make the amp piping hot actually) .

post #4196 of 10506
Quote:
Originally Posted by TrollDragon View Post

The problem with the filament windings is I really don't know if it would be safe to draw the whole 1A through one side or not. It all depends on the AWG of the wire used in the windings. If they designed this transformer so that each side only provided 500mA then drawing more than that would overheat the winding and one of the wires would burn open.

This transformer is custom made for LD so I am not sure if they would sell you a replacement or not, I have searched for a compatible replacement but I could not find any, it would have to be a custom wind, or you would have to find something that would fit the case and then modifications to all the heater connections would have to be done.

If you wanted to try high filament current tubes you can just roll the dice and hope you don't burn out your transformer or parallel the drivers heater wires together but that would require a scope to make sure the phase is correct. Pin 3&4 on all the different amps might not be hooked up the same way as there is no distinct markings on the wires.

 

So if I wanted to feel comfortable rolling 600ma double triodes, one possible solution is to parallel the heater wires together, that is, tie pin 3 on the left and right Vectors together and pin 4 likewise. However, there is a chance that these connections might be out of phase..... and I do not have an o'scope.... 

 

So a couple questions:

 

1) If connected out of phase and powered up, is there risk of damaging the tube and/or amp?

 

2) If there is no risk of damage, is it likely that one could tell empirically if the wires are connected in phase? Perhaps an out-of-phase connection would sound different, perhaps worse? If so, would this seem to be a reasonable course of action?

 

Thanks!

post #4197 of 10506

This is the final version of 6 v. adaptor  for 6DJ8 tubes.                                                                                                                                                                                                                                                                                   

post #4198 of 10506
Hey Gibosi!

If the windings are not connected in the proper phase and there is a small difference in the resistance of both windings the transformer will cook itself to failure. With today's toroidal core transformers the chances of a resistance mismatch is slim since the windings are wound at the same time. I could not possibly guarantee success or failure based on a few numbers off of a questionably made Chinese transformer.

The Chinese are well known for their lack of documentation and quality control.

Since you are running external tubes from a breadboard, I personally would locate on the internet a 120V Primary / 6.3V 2A Secondary transformer that you can hook up to AC and power which ever tubes you wish.

Basically you are moving the driver filament power off of the amp.
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Edited by TrollDragon - 12/3/13 at 1:34pm
post #4199 of 10506
Quote:
Originally Posted by TrollDragon View Post

Since you are running external tubes from a breadboard, I personally would locate on the internet a 120V Primary / 6.3V 2A Secondary transformer that you can hook up to AC and power which ever tubes you wish.

 

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! :) 

post #4200 of 10506
You are most welcome gibosi!

I would hate to read about someone burning out there amp or even worse expensive headphones, all on the chance that a $35 tube went south or was shorted right from the start.

Always test new tubes with a disposable pair of headphones, it's better to be safe than sorry.

All the pioneers like yourself and others in this thread who have broken new ground and rolled tubes not even imagined are to be commended.

Bravo guys, job well done!
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