[TrollDragon]

Was thinking of using Littledot mk3 as preamp with my Pioneer SX750 and i was told against doing this because of possible dc current surge any body here knows if the caps are dc blocking caps 
 this is from the vintage thread  .Thanks                                                                                                                                                                   

Hey MIKELAP, I was just reading about that over on DIY Audio.

The Pre Out of the LD I guess is very poorly designed. What I gather from reading is if the LD blows a tube there can be over 100V DC dumped out the Pre Out jacks, I had a look at the schematic for the SX750 and there are caps on the Aux In at the input opamps but it is a low value and only 25V.

So this is the dilemma, you can hook it up and as long as you don't have a bad tube all is good and it could last for years. The moment the tube goes bad and it starts dumping out DC that little 25V cap is not going to save the the SX750, smoke will roll and most likely your speakers with it.

What some have done is installed blocking caps on the inputs inside of their speaker amp as there is no room in the LD. They install 500uf 250V caps on the input line which will safeguard against a failure, but these caps are huge and $40 each.

It might be something to consider, but I would consult with someone who has more electronics knowledge than I have.

A Russian Roulette with your speaker system IMHO is just not worth the chance.

 

[MIKELAP]

Quote:

Hey MIKELAP, I was just reading about that over on DIY Audio.

The Pre Out of the LD I guess is very poorly designed. What I gather from reading is if the LD blows a tube there can be over 100V DC dumped out the Pre Out jacks, I had a look at the schematic for the SX750 and there are caps on the Aux In at the input opamps but it is a low value and only 25V.

So this is the dilemma, you can hook it up and as long as you don't have a bad tube all is good and it could last for years. The moment the tube goes bad and it starts dumping out DC that little 25V cap is not going to save the the SX750, smoke will roll and most likely your speakers with it.

What some have done is installed blocking caps on the inputs inside of their speaker amp as there is no room in the LD. They install 500uf 250V caps on the input line which will safeguard against a failure, but these caps are huge and $40 each.

It might be something to consider, but I would consult with someone who has more electronics knowledge than I have.

A Russian Roulette with your speaker system IMHO is just not worth the chance.

Thanks alot for the input wont risk it then 

 

[MIKELAP]

Here are the pictures gibosi on the tubes i marked the 2 and 4 pins according to page 77 PIN NUMBERING -BOTTOM OF TUBE VIEW - haltrons first 3picture then Siemens 3 pictures .if you need other views of the tubes let me know

 

[MIKELAP]

Quote:

Was thinking of using Littledot mk3 as preamp with my Pioneer SX750 and i was told against doing this because of possible dc current surge any body here knows if the caps are dc blocking caps 
 this is from the vintage thread  .Thanks                                                                                                                                                                   
 

 
Quote:

Hey MIKELAP, I was just reading about that over on DIY Audio.

The Pre Out of the LD I guess is very poorly designed. What I gather from reading is if the LD blows a tube there can be over 100V DC dumped out the Pre Out jacks, I had a look at the schematic for the SX750 and there are caps on the Aux In at the input opamps but it is a low value and only 25V.

So this is the dilemma, you can hook it up and as long as you don't have a bad tube all is good and it could last for years. The moment the tube goes bad and it starts dumping out DC that little 25V cap is not going to save the the SX750, smoke will roll and most likely your speakers with it.

What some have done is installed blocking caps on the inputs inside of their speaker amp as there is no room in the LD. They install 500uf 250V caps on the input line which will safeguard against a failure, but these caps are huge and $40 each.

It might be something to consider, but I would consult with someone who has more electronics knowledge than I have.

A Russian Roulette with your speaker system IMHO is just not worth the chance.

I sent an email to David zhezhe of Littledot regarding dc coupled amps  and this is his reply :      

The Little Dot MK III s not recommended to be used with DC coupled power amplifiers, which sounds like your SX750 is.

Best Regards,
David
 
[size=10pt] - davidzhezhe[/size]

 

[Audiofanboy]

Quote:

 
I sent an email to David zhezhe of Littledot regarding dc coupled amps  and this is his reply :      

The Little Dot MK III s not recommended to be used with DC coupled power amplifiers, which sounds like your SX750 is.

Best Regards,
David
 
[size=10pt] - davidzhezhe[/size]

 
This being said, I've used my MK IV SE countless times as a preamp with Tripath based power amps that most definitely are DC coupled.
 
I know this for a fact since when I use them as actual bridged power amps -"mono blocks" as they say, with no volume control- and the LD plugged to them and running, I can hear the DC offset, and it is loud, dangerously loud. Of course, it is, I mean, even 10-20 mV of offset straight into a 150W power amp with no caps would end up being loud on even slightly efficient speakers.
 
But if I use the integrated volume pots on the power amps -which I need to as otherwise I have about a mm of volume tracking using the LD pot- at, say, a quarter of the potentiometer, then the noise level -amplified DC offset- is OK, but not totally gone.
 
If it really gets bad, the power amps just switch off anyway, so what I'm doing isn't risky per se, but I can't really say it's that reassuring either... I do get great sound plugging the amps and preamp that way, as there's almost nothing on the signal path.
 
Mikelap, great pics of both tubes! So, can we conclude that they're the same? Have we solved the Siemens mystery? Are those foreign Siemens just Japanese Matsuschiita tubes?
 
If they are, then I've got some ebay browsing to do lol!

 

[gibosi]

Quote:

Here are the pictures gibosi on the tubes.......
 

 
 

 
This is very interesting...  It appears that Oskari's hunch was correct. You can see on both of these tubes that grids 2 and 4 are connected with a little strap above the top mica, on the left hand side of the tube. Also, the plates, seam and the location of the holes is the same on both of these tubes. They look to be identical. However, judging from the boxes and the etching on the tubes, the Siemens appear to be 1960s European production, while this Haltron appears to be 1970s or later. So while I do not think that the Siemens were manufactured in Japan, my best guess is that manufacturing equipment that was once used to produce these Siemens was relocated from Europe to Japan, and was then used to produce what are essentially the same tubes. Anyway, I would not be at all surprised if these tubes sound virtually the same as the Siemens and the Zaerix. Very interesting!!

 

[Audiofanboy]

Quote:

 
This is very interesting...  It appears that Oskari's hunch was correct. You can see on both of these tubes that grids 2 and 4 are connected with a little strap above the top mica, on the left hand side of the tube. Also, the plates, seam and the location of the holes is the same on both of these tubes. They look to be identical. However, judging from the boxes and the etching on the tubes, the Siemens appear to be 1960s European production, while this Haltron appears to be 1970s or later. So while I do not think that the Siemens were manufactured in Japan, my best guess is that manufacturing equipment that was once used to produce these Siemens was relocated from Europe to Japan, and was then used to produce what are essentially the same tubes. Anyway, I would not be at all surprised if these tubes sound virtually the same as the Siemens and the Zaerix. Very interesting!!

 
OK, should have seen this coming... Just typing "Siemens Matsuschiita" in google, there seems to be an obvious link between the two companies, at least historically and for component manufacturing. We may very well be pretty close to reaching a conclusion on the "Siemens" tubes.

 

[siles1991]

hey guys havnt been around for awhile still waiting for my mkiv se >.<!! in my collection atm is just Sylvania 5915 and the TS 6AH6WA, looking to find new tubes to add to my collection. Any really good tubes that can be found atm?
 
edit: oh yeah and the valvo EH90 as well in my collection

 

[duncan1]

An -EK90 is a hexode tube used in the front end of tube radio receivers.As  such having multiple grids it is more noisy than a triode tube - grids  2+4 are strapped together for use in radio design circuits One of the reasons for this is electron flow which has to go through multiple grids  some electrons bouncing off and creating noise . That is why communication receivers  [tube] usually had 1 or 2 RF stages before the FC tube so that the signal to noise ratio was large and so the effect of the noise was at a much lower level  Also in these communication receivers a lot of the time the FC tube [which carries out 2 functions] was separated and the oscillator was usually a separate tube..I wouldn't use one as the input to any tube amp.Special service tubes-used by government and military forces were made to a much higher standard than the normal commercial issues.they also had longer lives due to the cleaner conditions they were made under. Had rigid inspection and testing. 

 

[gibosi]

Quote:

hey guys havnt been around for awhile still waiting for my mkiv se >.<!! in my collection atm is just Sylvania 5915 and the TS 6AH6WA, looking to find new tubes to add to my collection. Any really good tubes that can be found atm?
 
edit: oh yeah and the valvo EH90 as well in my collection

 
The current "tube-of-the-moment" is the RCA 6DT6. And usually these are very cheap!

 

[siles1991]

Quote:

 
The current "tube-of-the-moment" is the RCA 6DT6. And usually these are very cheap!

would the 6DT6A's in this link be RCA's?
 
http://www.ebay.com.my/itm/NIB-new-vacuum-tubes-6D4-6DB5-6DC6-6DC8-6DE6-6DE7-6DR7-6DT5-6DT6A-RCA-6DT8-6DX8-/390478347313?pt=LH_DefaultDomain_0&var&hash=item5aea52bc31&_uhb=1#ht_500wt_923

 

[gibosi]

Quote:

would the 6DT6A's in this link be RCA's?
 
http://www.ebay.com.my/itm/NIB-new-vacuum-tubes-6D4-6DB5-6DC6-6DC8-6DE6-6DE7-6DR7-6DT5-6DT6A-RCA-6DT8-6DX8-/390478347313?pt=LH_DefaultDomain_0&var&hash=item5aea52bc31&_uhb=1#ht_500wt_923

 
Not necessarily...  It is likely that he has more than one brand in stock. You will have to send the vendor a message asking if he has two RCA.

 

[gibosi]

Tung Sol 6DT6
 
In order to get a handle on the sound of this tube, I pulled out the venerable Tung Sol 6485 to compare. The TS 6485 was configured in the EF95 2-7 strapping (we have no other choice as this is the only way we can use this tube in our Little Dots) and the TS 6DT6 in the EF95 1-7 strapping. The TS 6DT6 has the classic TS 6485 sound, with deep strong base, warm vocals and clean and detailed highs. The most obvious difference is in the sound stage. The TS 6DT6, similar to the RCA 6DT6, has a very wide sound stage, noticeably wider than the TS 6485. In my mind, with the wider sound stage, it is an improved version of our beloved TS 6485.
 
So if you like the sound of the TS 6485 (and/or TS 6AH6W/A), then the TS 6DT6 will very likely bring a smile to your face. Recommended.
 
Unfortunately, these are somewhat scarce, but they do turn up every so often, and they are not expensive. I paid $12 including shipping for my pair.
 

 

 

[TrollDragon]

Quote:

An -EK90 is a hexode tube used in the front end of tube radio receivers.
<SNIP>
I wouldn't use one as the input to any tube amp.

 
I thought, in my very limited knowledge about tubes that an EK90 was a Heptode with seven electrode's as opposed to a Hexode which has six.
And we should not be using these? But for the past XX number of pages here, everyone has been getting great results with the EK90's and EH90's.

 

[mab1376]

Whats the difference between the EH90 with ribbed plates vs the smooth plates?
 
I have the Valvo smooth plates and so far like them a lot.