[Olias of Sunhillow]

Quote:

7308 can be used as a replacement for 6922's, right?  If so, should be fine.  I haven't personally tried them myself, though, and someone with more knowledge and experience can correct me.

 
Well, that was a sort of vague response from Cavalli. I've never encountered a situation where a 7308 couldn't sub for a 6922, but I'd love to have that confirmed by the manufacturer.
 
I probably wouldn't try something like a 6N1P or 6BZ7 without explicit approval from Alex.
 
 

 

[Equus]

Haha...I don't think he was meaning to be vague.  That email string was from around the time the initial batches of LF's were going out the door and I think sleep deprivation was striking our kind doctor.

 

[clifwst]

I asked the same question, and he said they should work. 
 
The 7308 is the same inside as a 6922, except the two sides are closely matched to each other.  That was important for some of the military applications the tube was originally used for. Between tubes the tolerance for 7308s was also closer then between generic 6922s for the same reason.
 
From, here;
 
http://www.audiotubes.com/6dj8.htm
 
Quote:

7308:

This is probably the ultra 6DJ8 type tube commonly available. It has all of the features of the 6922, but the triode sections are also matched to each other, and the tubes all fit within very tight specifications. Therefore, any 7308 should match any other 7308 within the same brand. The Amperex versions were again made in New York, complete with gold pins, and often have a number etched into the side of the glass. Amperex made these for industry as well as the military. The Amperex versions have the PQ label, the military type usually is labeled "USN-CEP", but I have seen versions made for Stromberg-Carlson and Hewlett-Packard, with white ink labels. These all had the numbers etched into the glass, and all are the same tube. The USA made military white label types have been rated "Best of All", over other 7308, 6922 and even Cca tubes, in several well-documented 6922/7308/Cca listening tests. Therefore this particular type is becoming scarce and prices are rising. There were a few of these made in Holland, but most were made in the USA, therefore the Holland tubes are RARE and usually command a higher price. The Holland PQ versions have the PQ with stars on either side of the letters, and the words "Premium Quality", where the USA types have the PQ inside of a shield logo. Again, there are some nice vintage USA made standard pin military and industrial types available from Raytheon and Sylvania, just to name a few, and these are quite good at a price currently far below the European vintage labels. Finally, Philips (the parent company of Amperex) owned a number of tube brands, and many were never seen outside of Europe. Most were actually made in the same Heerlen, Holland factory that turned out the Bugleboy 6DJ8 and PQ 6922 Amperex. Watch for tubes labeled E188CC with brands like Valvo, R/T, RTC, Miniwatt, Dario, Philips, and Adzam. These tubes are identical to the Amperex PQ and Philips SQ (Special Quality) types more often found in America, and are perfect if the Amperex label is not available. Also rare in America are these same brands made at the Philips-owned Mazda factory (La Radiotechnique) in Suresnes, France. These usually have a capital "F" in the second line of the date code. They are sweet like the Holland tubes, with a bit better detail and punch at the top end, and still have nice balanced warmth. We are one of the very few worldwide tube dealers to offer these rare NOS French Philips tubes. Finally, watch for Siemens or Telefunken German made 7308 tubes, most having the E188CC label in white, with the Telefunken having the distinctive diamond shape in the bottom glass. Siemens are usually more plentiful, and a huge savings over their Cca tubes.
 

 

[dBel84]

Quote:

A quick question: do 7308s work on the Liquid Fire?

 
Quote:

 
Well, that was a sort of vague response from Cavalli. I've never encountered a situation where a 7308 couldn't sub for a 6922, but I'd love to have that confirmed by the manufacturer.
 
I probably wouldn't try something like a 6N1P or 6BZ7 without explicit approval from Alex.
 
 

I am not the good Dr Cavalli but we have had many discussions about this amp and tube options and probably more so concerns when it comes to the Liquid Fire and tube options. This was perhaps more relevant after I started looking into the datasheets of some of the tubes out there. The Phillips PCC88 flagged my attention. The data sheet I initially had was a composite of many 6DJ8 tubes and had abbreviated data, the actual datasheet however shows that the 2 triode sections do not have the same tolerances. The circuitry in this amp relies on very tight tolerances , thus beware of tubes that are beyond their prime, cheap copies of the 6922 or tubes that do not match the 6922 tolerances closely enough in both of the triode sections. Good tubes will function perfectly for many years as the circuit does not unduly stress the tubes and the amplifier has 3 safety circuit additions to protect it.
 
This is why AC has advocated from the beginning to be careful with tube rolling in the Liquid Fire. Most of the tubes substitutions have followed this logic in that only good quality 6922/6DJ8 NOS tubes have been used. The 7308 falls into this category. The 6n1P does not. Unlike some other hybrid amplifiers which are "a tube rollers dream" , the LF is designed to much tighter tolerances and thus needs the tubes to work within these margins. 
 
..dB

 

[googleli]

One more side question. From the pictures, the tubes seem to be located at the front of the amp, but do I need to open up the amp to change the tubes? If opening is required, what kind of screwdriver do I need to open it up? I am asking because the LF will be delivered to my office and I will have to prepare in advance to bring in the tubes from home and a screwdriver to open it up (if needed) since I want to change the tubes once I receive the LF. Thanks!

 

[mwilson]

6 screws at the bottom, easily removed using a standard Phillips driver. The cover slides back, and you don't have to completely remove to change tubes.

 
Quote:

One more side question. From the pictures, the tubes seem to be located at the front of the amp, but do I need to open up the amp to change the tubes? If opening is required, what kind of screwdriver do I need to open it up? I am asking because the LF will be delivered to my office and I will have to prepare in advance to bring in the tubes from home and a screwdriver to open it up (if needed) since I want to change the tubes once I receive the LF. Thanks!

 

 

[Clayton SF]

Quote:

... The circuitry in this amp relies on very tight tolerances , thus beware of tubes that are beyond their prime, cheap copies of the 6922 or tubes that do not match the 6922 tolerances closely enough in both of the triode sections. Good tubes will function perfectly for many years as the circuit does not unduly stress the tubes and the amplifier has 3 safety circuit additions to protect it.
 
... the LF is designed to much tighter tolerances and thus needs the tubes to work within these margins.   
..dB

Which shows how highly Dr. Cavalli regards the stock JJ tubes. You don't have spend a lot on tubes to get incredible music in return. Most of the glowing LF reviews come from the LF with stock tubes (from which I have yet to veer).
 

 

[mwilson]

OK, I'll bite. The JJs came out before I even powered on the LF, and I went to Siemens after a brief Tungsram detour. I'll put the JJs in one of these days and will give them a listen. I'll report back.

 
Quote:

Which shows how highly Dr. Cavalli regards the stock JJ tubes. You don't have spend a lot on tubes to get incredible music in return. Most of the glowing LF reviews come from the LF with stock tubes (from which I have yet to veer).
 

 

 

[runeight]

Quote:

One more side question. From the pictures, the tubes seem to be located at the front of the amp, but do I need to open up the amp to change the tubes? If opening is required, what kind of screwdriver do I need to open it up? I am asking because the LF will be delivered to my office and I will have to prepare in advance to bring in the tubes from home and a screwdriver to open it up (if needed) since I want to change the tubes once I receive the LF. Thanks!

Just to quickly offer this thought. Turn the amp on and run some music through it before swapping tubes. I know it worked when it left me, but things happen in transit.

 

[Soned]

This is probably a stupid question, but what should the lifetime be for the LF?

 

[runeight]

I'm not sure that I can answer this in this forum since I am operating as MOT and cannot promote my products. Mods will, of course, edit or delete as per the rules.
 
If we look across the broad array of audio equipment there is a wide range of lifetimes. Most well done equipment lasts many years.
 
Tubes can last anywhere from 1000 hours (sometimes even less) to 10,000 hours. Tubes in power stage circuits or where the tube is pushed to the edge of its operating envelope can have pretty short lifetimes. Tubes in very light duty relative to their specs can last 10, 000 hours. Solid state components if used properly and cooled properly can last longer than any of us may live.
 
What affects lifetime in any piece of equipment is the circuit design itself, operating points, component choice, and ventilation (and of course how it is treated by the owner).
 
All that I think I properly say is that we have tried to make a smart circuit design that keeps all of the components within operating bounderies. We have tried to choose durable components that support the SQ. For example, the LF gets pretty hot so all of the electrolytics are 105C to extend their useful lives. The LF has lots of ventilation for the same reason using the vent holes on the top as part of its design look. The LF has a startup sequence that ensures that the tubes are conducting before applying the rails. This prevents cathode striping (caused by plate voltage with cold heaters) and allows the circuit to come up gently instead of slamming to one of the rails while waiting for the tubes to warm up. Etc. etc.
 
So, in the design and implementation we have endeavored to make a durable, solid amplifier. In truth the only full test of this will be how the amps do over time in service to their owners.

 

[googleli]

Thanks doc, I will try it with the stock tubes first before doing anything. Also thanks for the extra efforts in rewiring it to 220V. Cheers!

 
Quote:

Just to quickly offer this thought. Turn the amp on and run some music through it before swapping tubes. I know it worked when it left me, but things happen in transit.

 

 

[wuwhere]

Quote:

I'm not sure that I can answer this in this forum since I am operating as MOT and cannot promote my products. Mods will, of course, edit or delete as per the rules.
 
If we look across the broad array of audio equipment there is a wide range of lifetimes. Most well done equipment lasts many years.
 
Tubes can last anywhere from 1000 hours (sometimes even less) to 10,000 hours. Tubes in power stage circuits or where the tube is pushed to the edge of its operating envelope can have pretty short lifetimes. Tubes in very light duty relative to their specs can last 10, 000 hours. Solid state components if used properly and cooled properly can last longer than any of us may live.
 
What affects lifetime in any piece of equipment is the circuit design itself, operating points, component choice, and ventilation (and of course how it is treated by the owner).
 
All that I think I properly say is that we have tried to make a smart circuit design that keeps all of the components within operating bounderies. We have tried to choose durable components that support the SQ. For example, the LF gets pretty hot so all of the electrolytics are 105C to extend their useful lives. The LF has lots of ventilation for the same reason using the vent holes on the top as part of its design look. The LF has a startup sequence that ensures that the tubes are conducting before applying the rails. This prevents cathode striping (caused by plate voltage with cold heaters) and allows the circuit to come up gently instead of slamming to one of the rails while waiting for the tubes to warm up. Etc. etc.
 
So, in the design and implementation we have endeavored to make a durable, solid amplifier. In truth the only full test of this will be how the amps do over time in service to their owners.

 
I have a 27 years old ARC D-70 all tube amplifier (5 6550s). I've only replaced the tubes and the big power supply electrolytic caps (Mallory 800mfd). I took the cover off for better ventilation.
They can last. BTW I'm using it to power my HE-6.

 

[Icenine2]

I played a Mesa Boogie guitar amp from 1978-2010.  Custom built.  32 years!  I changed the power tubes once and I played the heck out of this thing and it went to the studio with me and back and to gigs.  I had an amp guy fix a buzz I got in it once and that was it!  32 years!  I read where Jeff Beck has an amp he uses/used that the tubes are stuck in their unless you pull everything apart and it still works fine.  So lifetime of amps could be quite a while.

 

[wuwhere]

That's what you can call over engineered. Time is the best  test .