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New Cavalli Audio Liquid Glass Amplifier - Fall Release - Page 15

post #211 of 637
Quote:
Originally Posted by dBel84 View Post

adapters to be able to use your 6F8G's ;-)      like these http://www.head-fi.org/t/624548/woo-audio-6sn7-to-6f8g-tube-adapters

 

..dB

 

The adapters are also on order.

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post #212 of 637
Thread Starter 

Gents, I gotta tell you, manufacturing stuff is not for the faint of heart.

 

LG run is in full swing. So I visit the PCB assembly shop to verify the first finished board. HV works great. LV works great. Left channel buffer is good. Right channel buffer is a mess.

 

What happened? Did I make an error on the board going from the proto to the production board? Measuring voltages, pulling transistors, trying to find the likely cause of the problem. People waiting for amps, lots left to do to get them out the door. Nothing. Nada.

 

Go home, look at the schematic for an hour. No ideas. Look at the board layout. Nothing. Starting to panic. Maybe the design sucks. Maybe the pre-production amp was just a fluke.....

 

Then I visit the shop very early the next morning after being up late. Finally I see that they have swapped the NPN/PNP devices at the input to the right channel buffer. So we swap those and, bang, comes right up exactly the way it's supposed to.

 

Geez.

post #213 of 637

One of your builders always tosses a wrench in your plans, Alex. Glad you got it sorted out.

post #214 of 637

Does it mean we still expect delivery around Nov? 

post #215 of 637
Thread Starter 

The original delivery date was scheduled for about middle of Nov. I think we'll be close, but probably slightly delayed.

post #216 of 637
Thread Starter 
Quote:
Originally Posted by preproman View Post

Yeah - I know and my bad.  It doesn't seem like it's much interest in it to start a new thread.  I'll do it anyway, what the hay..



Here is a little status. I believe we have resolved the issue that Don ran into before RMAF. This required new boards, however, and a new build. I have built one board to test out the fixes. As of last night all seemed to be fixed. Now I have to build up the second board. If this comes up without problems then we can begin to believe that we have resolved the issues.

 

If we got two working boards, we can complete the proto and find out if the amp has the chops that I think it does. If it does, well then I'd love to send it around..... biggrin.gif

post #217 of 637
Quote:
Originally Posted by runeight View Post



Here is a little status. I believe we have resolved the issue that Don ran into before RMAF. This required new boards, however, and a new build. I have built one board to test out the fixes. As of last night all seemed to be fixed. Now I have to build up the second board. If this comes up without problems then we can begin to believe that we have resolved the issues.

 

If we got two working boards, we can complete the proto and find out if the amp has the chops that I think it does. If it does, well then I'd love to send it around..... biggrin.gif

 

 

OK very cool.  I'll be more than happy to volunteer for testing..

post #218 of 637
Quote:
Originally Posted by preproman View Post

I'll be more than happy to volunteer for testing..

 

Quick, attach the electrodes to his nipples before he changes his mind!

post #219 of 637

Doing a bit of tube research lately and stumble in a tube BL63.  Do you guys think it will work with the LG?  It seems people with Balancing Acts raves about them.  But since it has higher requirements from a 6sn7 its might be a toss up.  Even the size of the tubes might be tight fit for the LG.

700

post #220 of 637
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post #221 of 637
Quote:
Originally Posted by Neogeo333 View Post

Doing a bit of tube research lately and stumble in a tube BL63.  Do you guys think it will work with the LG?  It seems people with Balancing Acts raves about them.  But since it has higher requirements from a 6sn7 its might be a toss up.  Even the size of the tubes might be tight fit for the LG.

700

 

I had responded to NG333's pm before seeing this, the BL63 has a heater requirement of 1.3amps per tube making it unsuitable for the LG - this is just too much current. Most of the tubes rolled through this amp will use 300mA or 600mA. The low plate voltage of the BL63 is not an issue  - it is optimized to run at 100V on the plate with a max of 200V , not unlike a 6922 tube. BUT as stated, that heater current is a deal breaker. 

 

..dB

post #222 of 637
Thanks db84. Almost got me a pair of bl63. Still i wish theres some kind of simple non threatening mod that can be applied to the LG to make them work.
post #223 of 637

If you are looking for rare , but glorious sounding tubes , try and find the Mullard CV181 - these have a higher heater requirement too but are within the spec for the LG..dB

post #224 of 637
Thread Starter 

Gents, now that we are approaching delivery of some of the LGs and some of you are buying tubes, here are some guidelines. This info will all be in the user manual.

 

Don't forget that the tubes must have either 6sn7 or 12au7 pinouts or an adapter that conforms to this.

 

The total draw from the heater supply is limited to 1A. This covers A LOT of tube types.

 

Be aware, however, that tube heaters are run in series when they are 6V and  parallel when they are 12V.

 

So, the maximum heater current for 6V tubes per tube is 1A. But, the maximum current per tube for 12V tubes is 500mA because they are in parallel.

 

The LG has two plate voltages, 300V and 200V.

 

The triode pair in each bottle is in what is called a totem pole configuration. This means that each triode section see half the plate voltage. Thus, with 300V each triode sees 150V and, obviously, with 200V each triode sees 100V. The totem pole is what allows the front end to self-adjust to many different kinds of tubes.

 

Also, the gain of the amp is 1/2 the mu of whatever triode is used.

 

Most of the tubes that you will use will be at the 300V setting (certainly 6SN7s and 12AU7s and equivalents). But some, like 6922 can only handle a max of about 130V on their plates. Thus, for these tube types I've provided the 200V setting (100V per triode).

 

Then there are weird beasts like 6H30. 6H30s pushes the amp to its limits in every possible way. Their heater current is 800mA. Definitely within the amp's abilities because they are 6V tubes, but still high.

 

However, 6H30s can run at 150V. But if they do they suck huge amounts of plate current when biased the way they would be in the LG. Hence, even though 6H30s can be run at 300V the MUST be run at 200V in order to control their plate current. This may be true of other tubes that we are not yet familiar with.

 

It would have been possible to provide adjustments for this, but then the amp would have literally become a tube tester and you would have lost the fairly simple plug and play operation that it has now.

 

Don and I will try to provide lists of tubes that should work (see website) and you'll need to exercise some care in choosing and running tubes, but for the most part things should be fairly simple.

 

Also, the LG HV supply has a shutdown feature if the plate current is too high. The amp will simply shut off.

 

And, the one heater mistake that you can make is to put 6V tubes in with the 12V heater setting. If you're paying attention you will see this immediately since the tubes will start to glow like a light bulb. Normally if you turn them off quickly they won't be damaged.

 

If you exceed the max heater current the amp will, eventually, fail. Maybe not right away, but the heater supply will just get too hot.

 

But, if you are thoughtful and careful you should be able to roll a lot of tubes through this amp.

post #225 of 637

Its getting close to release.  I am new to tubes and dont have a single pair. 

 

Can anyone recommend a good pair or two for me?  Maybe one octal and one noval. Thanks

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