Triode ST 70 Bias Expansion

knowledge base for the classic Dynaco ST70

Postby burnedfingers » Sat Aug 04, 2012 1:46 am

I copied this off the web site of SND tubes




Do you use 6L6's or 7027A's? Do you like American made ones but don't like the price of $65 or more? Then you need to CHECK THIS OUT!
We have procured a VERY large supply of new old stock Philips/ECG (formerly Sylvania) 6BG6GA tubes that are PERFECT replacements for any 6L6 or 7027A. In cases where the amplifier connects the cathode to G3 (suppressor grid), you can even use these in place of EL34/6CA7 tubes. (I am currently using them in my Eico HF-89 amplifier and Bogen MA-265 amplifier). These improved 6BG6GA tubes are ABSOLUTELY IDENTICAL to the Sylvania 7027A/6L6GC because they were made with exactly the same components. They have the larger 35 watt plates found in only the 7581A/6L6GC or 7027A which means they will work in ANY 6L6 or 7027A application. The difference between the 6L6 and this 6BG6GA is the 6BG6 has the plate connection at the top of the tube, so it has a "cap". Because the plate connection is at the top, this tube can easily handle plate voltages in the 700Volt range. There are also 2 wires reversed in the tube base. Ok what is the advantage? PRICE!! While new 7027A's are $45+ each and 6L6GC's are $65 each (or more), our 6BG6GA's are only $12 each!! We are offering adapter kits to convert 6BG6's to 6L6's or 7027A's for only $10 each (they only differ in the way they are wired). You simply plug the adapter into the tube socket on your amplifier and then plug in the 6BG6. These work and sound EXACTLY like Phillips/Sylvania 6L6GC's. We have already sold quite a few of these and almost everyone who has bought them has reordered more of them. With the supply of NOS tubes disappearing at an alarming rate, you can still afford to lay in a lifetime supply of these quality tubes.

FAQ's
The published specs say that 6BG6GA's have a plate dissipation of 19 watts. How do you know that these tubes have a 35 watt plate dissipation?

I've been asked this one allot. I set the Philips/ECG tube up on my General Radio Vacuum Tube Bridge. I cranked the power supplies up to run the tube at maximum ratings..(500VDC plate voltage, 75ma plate current=35W). Screen voltage was set at 450 VDC. I allowed the tube to run continuously for several hours. There were no red spots on the plate and the tube operated absolutely normally. I did this for several samples. I also set the tube up to run maximum screen dissipation (5W). No problems. I then tried several different NOS 6BG6GA's from the 60's. The all IMMEDIATELY had large red spots on the plates AND FAILED within minutes. Furthermore, I have been running these tubes in my own personal amplifiers. One is a Bogen 65W per channel amp which was designed to use 7027A's. It runs 540V on the plate. These tubes have been running for several hundred hours in this amp with absolutely no problems at all.

Can I use the older 6BG6's that I have on hand already? The answer is MAYBE. If you use them in an application that calls for earlier versions of the 6L6,(6L6, 6L6GA, 6L6GB, 6L6WGB, 5881), then they will work fine. I do not recommend the older tubes for amps that call for 6L6GC/7581A/7027A. These older 6BG6GA's have 19 watt plates and will not work for these tubes.
burnedfingers
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