[lemonjelly]

  Thats exactly what i was told when i wanted to use my LD mk3 with my 70's Pioneer. I was told tough that the LD MK9 can be used with DC coupled amps .

 
Hi lemonjelly,
 
I have a DC coupled receiver that I cannot use with the MKIII.  Do you know of any kind of circuit or outboard unit that can be added to block the high DC voltage?
 

Hi yep I think they included a DC protection circuit in the later amps.  If someone wanted I would think you could do this yourself + add it to the chain.  Probably there would be 2 ways of doing it, either after the DC coupled power amp with something like this (http://www.ebay.co.uk/itm/2X-Stereo-Speaker-protection-DIY-kit-Dual-relay-with-startup-delay-DC-protection-/221390943192?pt=US_Home_Audio_Amplifiers_Preamps&hash=item338bedb3d8) or after the LD with something like this (http://www.ebay.co.uk/itm/MINI-UPC1237-Headphone-Protector-Protection-For-Headphone-Amplifier-AMP-Project-/150784726223?pt=UK_Sound_Vision_Other&hash=item231b7854cf).  They just kick in once the DC voltage gets above a certain level, so you're not using the circuit all of the time, but it just gives you insurance that your speakers will be protected.
 
I'd guess really that you'd be best using the speaker protection version as I wouldn't be sure what voltage would be safe to be amplified by the power amp (and would depend on the power amps volume/gain I would think).  The other problem is potentially that the DC offset, even below a dangerous level might still be enough to degrade the sound (it isn't a good thing even in moderation).  
 
Edit: just read a bit more about this (there's a good audiok thread if you google for dc offset blown speaker), so it seems you'll always have a bit of offset with a DC coupled amp anyway, and you can check to see how much that is with a multimeter.  I suppose with the speaker protection board above, you would protect your speakers from any bad tube problems, and you could check what the DC offset is with/without the LD connected to see if the DC offset changes much, and use your ears ofc to see what you prefer.

 

[hypnos1]

Hi guys.
 
Although at the moment I'm all caught up with the Feliks-Audio project, I still like to see what's going on here! (By the way, the new prototype will have the protection circuit for DC direct coupled amp use...).
 
And even though this is an old topic, I have just noticed that the famous GLENN has a unit at $2,500, and he's using the C3g as drivers...so must be a pretty good tube, eh?!

..

 

[mordy]

Hi LJ,
 
Thanks for your reply. I am a little bit confused, because I don't know what I need, either something to protect my DC coupled receiver, my speakers, or both.
 
I have an Outlaw RR2150 100W ss receiver. I used it with the LD MKIII as a pre-amp successfully for several years. One day one channel blew in the receiver. I had it repaired, but did not realize that I had blown one of my speakers. When connecting the speaker, the receiver blew again.
 
The speaker was replaced under warranty, the receiver repaired again (they did not charge me the second time), but I am afraid to use it with the LD amp.
 
Is seems to me that I need something between the LD and the receiver. At this time time the LD is connected to the receiver with RCA interconnects to an external (equalizer) loop.
 
All the various modules I looked at are inexpensive enough and usually DIY. One manufacturer will sell you a finished unit for another $4.00.
Could you look at these offerings and tell me what I need? How do I connect it?
 
http://www.ebay.com/sch/i.html?_odkw=1237+protection&_from=R40&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.X.TRS5&_nkw=Stereo+Speaker+protection+kit+Dual+relay&_sacat=0
 
http://www.ebay.com/sch/i.html?_from=R40&_trksid=p2050601.m570.l1313.TR0.TRC0.H0.X1237+protection.TRS0&_nkw=1237+protection&_sacat=0
 
Or do I need something else?
 
Presently I am using a 1980's Sony 110W ss amp. This amp has a built in protective relay. It's quite nice, but the RR2150 has many more features and I would like to use it without worry.

 

[lemonjelly]

  Hi LJ,
 
Thanks for your reply. I am a little bit confused, because I don't know what I need, either something to protect my DC coupled receiver, my speakers, or both.
 

Hi, cos I'm not using my LD as a preamp I haven't really looked at any of this before... but it's interesting so I'll have a read on stuff over the weekend and see if we can work it out (hopefully other people will also chime in).  I wasn't sure if an amplifier would become damaged or not by DC being passed, but it seems like that can be the case, so if we can put in a circuit to avoid too much DC being passed from the LD that would probably be the best plan.
 
The relays you linked to will protect your speakers (they kick in when DC goes over 1v for a lot of those circuits) but whether that means the amp will still blow or not I'm not sure.  It seems like the options are basically first add a capacitor in series to block any DC going to the receiver (in between the ouput RCAs from the LD and the input RCAs to the receiver).  Or add a relay which kicks in when the DC goes over a particular value (which will depend on the gain of the receiver).  If you add the capacitor in then potentially you're making the sound worse - this is why the DC coupled amp doesn't have any input capacitors in the first place.  But this shouldn't make much difference depending on the value (determining the frequencies passed) and quality of the capacitor (film etc would be best).  The relay would still allow some DC through which could make the sound worse just because speakers don't like DC.
 
After just looking briefly maybe adding an input capacitor in between the amps would work best... but I'll have a more thorough read over the weekend.
 
Edit: and an easy way of seeing the offset from the LD is to use a multimeter and connect to the +ve/-ve coming out of the amp - easy if you have senns as you can just put the probes on the spade connectors of each channel.  Or not cos actually you need a load to get accurate readings .... so have headphones plugged in and take the measurements from the RCAs.

 

[i luvmusic 2]

I can see fireworks.......

 

[mordy]

Hi,
 
Over on the Feliks Audio thread people are extolling the virtues of the 6N13S Svetlana Tubes with a winged "C". Did anybody compare them to the Chatham 6AS7G tubes?
 
If I decide to get a pair, which years and production should I look for?
 
After a lot of trial and error I must admit that I am partial to US made tubes, but I am open for suggestions.....

 

[i luvmusic 2]

 

Is these the one?Less bass and treble compared to RCA 6AS7G's but i like this 1960's Svetlana Winged "C" 6H13C for vocals/mids.
BTW these was my first 6AS7G tube and paid $6/tube + shipping.

 

[genclaymore]

I bought some mullard CV4010 off ebay and so far I liking them,I don't know how to explain how it sounds but the first thing I notice was the mids and then the bass impact, I liked the 6J1P-EB's but the details was a bit too much. Seems like the CV4010 sound imaging is different too, I not sure how to say it. Go it from a usa seller and it was a tad cheaper then the seller who was outside of the usa, that had the CV4010. I fear this vacuum tube swapping is gonna be like my op-amp rolling past, with  dozen of boxes of tubes in the closet, falling all over the place.

 

[gibosi]

  .............I fear this vacuum tube swapping is gonna be like my op-amp rolling past, with  dozen of boxes of tubes in the closet, falling all over the place.

Only dozens of boxes? Probably more like hundreds of boxes! lol

 

[mordy]

Hi,
 
Just got this tube with a new type of tube designation. What kind of tube is it? (The tube was made in Dec 1971)
 

Hint: It is not that difficult to figure out, but why?

 

[mordy]

Hi genclaymore,
 
Why don't you rely on the tube rollers on this forum that tried dozens and hundreds of tubes - one of the best (and least expensive) tubes that can be used without any modifications is the Ei 6HM5. [Plug and Play]
 
http://www.ebay.com/itm/6HM5-EC900-Lot-of-four-4-tubes-EI-Yugoslavia-NOS-free-shipping-/251611916081?pt=Vintage_Electronics_R2&hash=item3a953d2731
 
In the past it was possible to buy them for $5 each incl shipping. Nothing lost in making a low ball offer......

 

[gibosi]

  Hi,
 
Just got this tube with a new type of tube designation. What kind of tube is it? (The tube was made in Dec 1971)
 

Hint: It is not that difficult to figure out, but why?

 
That is bizarre! EFHGWA = 5687WA, but indeed, why? lol  And from the internals, the anodes, the getter support plate, the reinforcement rods and the copper grid posts, I would say it is a Sylvania.

 

[mordy]

Hi G,
 
You scored 100 + bonus points for figuring out that it is a Sylvania! My guess is that the tube people got frustrated when the tube era was ending and made strange designations. I actually have a tube, Sylvania as well, with a date code XYZ!

 

[MIKELAP]

  I bought some mullard CV4010 off ebay and so far I liking them,I don't know how to explain how it sounds but the first thing I notice was the mids and then the bass impact, I liked the 6J1P-EB's but the details was a bit too much. Seems like the CV4010 sound imaging is different too, I not sure how to say it. Go it from a usa seller and it was a tad cheaper then the seller who was outside of the usa, that had the CV4010. I fear this vacuum tube swapping is gonna be like my op-amp rolling past, with  dozen of boxes of tubes in the closet, falling all over the place.

What you need is this  case or a couple of them lol it goes fast and if you start with the 6AS7 and 6080 tubes type youll run out of room fast since that picture was taken  i filled up another case with the bigger tubes                                                                                                                                                                                  
 

 

 

[mordy]

Found a less elegant way of storing my tubes, but definitively less expensive. I use old shoe boxes where the contents are marked with a sticker. These are easy to stack, but here they are laid out to show the concept. This is maybe a third of the boxes I have.

 
Each box is marked with the contents:
 

 
Each individual box tube box is marked with what's inside. This is handy since oftentimes the markings wear off, even when handled gently.
 

 
Many of my tubes lack boxes. The little paper with designation, dates and notes is attached to the tube with a rubber band. The paper comes from an adding machine roll. When using the tube the paper is taken off.
 

 
With so many tubes it is hard to remember what is what. I am sure that there are many other ways to organize the tubes, but this simple system works for me.
 
Nic, how do you find what you are looking for among your 7000 tubes? (I only have around 400)