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Class A or ??????? http://dcaudiodiy.com/phpBB3/viewtopic.php?f=5&t=569 |
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Author: | J-ROB [ September 14th, 2015, 9:22 am ] |
Post subject: | Re: Class A or ??????? |
Another really intriguing tube is the Bendix 6977. This is a 9 pin mini single carbon plate low mu pass tube, like half of a 6080. Insanely well made. I have a pr that I d like to get into a line stage someday. http://frank.pocnet.net/sheets/131/6/6877.pdf BTW: Here's an interesting document on 6AS7s for audio http://www.clarisonus.com/Archives/TubeTheory/6AS7G.pdf RCA forbids paralleling sections but they don't spell out why. I guess they don't like OTLs. |
Author: | Roscoe Primrose [ September 14th, 2015, 9:39 am ] |
Post subject: | Re: Class A or ??????? |
Quote: Another really intriguing tube is the Bendix 6977. I've got a bunch of 6336As I'd like to play with sometime Still have at least 10 NOS 5998s as well.... J-ROB wrote: RCA forbids paralleling sections but they don't spell out why. I guess they don't like OTLs. In my experience 6AS7s/6080s don't typically match very well section-to-section. Without some means to balance the currents in each section, one section is going to end up with all the current... Roscoe |
Author: | Stuart Polansky [ September 14th, 2015, 9:41 am ] |
Post subject: | Re: Class A or ??????? |
One ohm plate resistors are what Atma-Sphere suggests and uses. |
Author: | Roscoe Primrose [ September 14th, 2015, 9:43 am ] |
Post subject: | Re: Class A or ??????? |
Stuart Polansky wrote: One ohm plate resistors are what Atma-Sphere suggests and uses. Those are there as fuses, 1ohm in the plate circuit isn't going to do a damn thing to balance the currents.... Roscoe |
Author: | J-ROB [ September 14th, 2015, 9:52 am ] |
Post subject: | Re: Class A or ??????? |
You are correct, Roscoe. I think Ralph sorts the Russian 6AS7s he uses in the Atma-Spheres. I think the 1 ohm resistors are test points for current balance. I've heard stories of runaway grid current issues with these tubes also. The specified 1 meg grid max resistance might be optimistic and invite problems. That is one of the things I liked about the Sears design, control and balance are designed in. |
Author: | Guy [ September 15th, 2015, 8:50 am ] |
Post subject: | Re: Class A or ??????? |
Stuart, Couldn't you use a 3.6K:8 output transformer if you don't want to go OTL? Maybe this winter I'll finish my phono amp, then start back on a 6AS7 OTL test bed. |
Author: | ratbagp [ September 15th, 2015, 9:05 am ] |
Post subject: | Re: Class A or ??????? |
I poked around in my stash of stuff and discovered I have most of the stuff required to build the Shoog DC7 Mk II so I have ordered the few parts I need and have started building. Naturally the fit and finish will be down at my usual woeful level. http://www.diyaudio.com/forums/tubes-valves/160059-dc7-mkii-new-schade-6080-amp.html Ebay has provided a pair of the 12L8GT for 99 cents plus shipping and I have a few 6080's. ray |
Author: | Stuart Polansky [ September 15th, 2015, 11:13 am ] |
Post subject: | Re: Class A or ??????? |
ratbagp wrote: I poked around in my stash of stuff and discovered I have most of the stuff required to build the Shoog DC7 Mk II so I have ordered the few parts I need and have started building. Naturally the fit and finish will be down at my usual woeful level. http://www.diyaudio.com/forums/tubes-valves/160059-dc7-mkii-new-schade-6080-amp.html Ebay has provided a pair of the 12L8GT for 99 cents plus shipping and I have a few 6080's. ray Awesome, I can't wait to hear it! Now we are talking about a meet! As for the cosmetics, well there are lots of us bottom feeders who don't mind at all! In fact, some of us are angry at the high bar set by some of the club members! LMAO! Kind of like the other cops are pissed at the cop who writes the most tickets! |
Author: | dberning [ September 15th, 2015, 8:19 pm ] |
Post subject: | Re: Class A or ??????? |
Stuart, You don't have to do the ZOTL, but as Guy suggested a 3.6 k P-P output transformer can be used to get the equivalent operating load as I do in the ZOTL. Now I like to light-load the tubes, and this is why my power went up when I loaded my amp with 4 ohms. The ZOTL is an ideal output transformer emulation circuit, and they are basically equivalent except the ZOTL reduces the problems associated with output transformer parasitics. My 3.6 k loading becomes 1.8 k P-P loading with a 4-ohm load. So you can pick an output transformer in between these figures and the 6AS7 will work just fine. You can supply the center tap of the transformer with 184 V if you ground the cathode, and apply a grid bias of - 80 V and you should match my operating conditions. David |
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