looking for ideas amp build

[mark enger]

i have a pt it runs 2 5y3 4 6v6 2 12ax7. it came out of a magnavox console stereo. i was thinking 18 or 36 marshall. but id rather use the octal sockets i already have. i iv built a nice 17 1/2 by 11 1/2 by 2 chassis i built at work to day it came out real nice. its ready for drilling. any ideas??? iv got a nos pair national 6l6 tubes i have been dying to try

[tubeswell]

Dual 5E3?

Or with the two rectifiers the Rectifier winding must be rated at least 3.8A - in which case you could run a whole variety of rectifiers. And the heaters will be rated for at least 2.4A (heck probably 3A - who rates a winding at 2.4A?) - enough for a couple of 6L6s and 2 or 3 pre-amp tubes - so you could build something like a BF Princeton Reverb or a Tweed Bassman

You could probably add another pre-amp tube without too much worry

[Chuck H]

The OT may not be ideal for a pair of 6l6 tubes. Not ideal doesn't mean you can't use it. It just won't be ideal. It also depends if you want to emulate a particular amps character. 6L6's and 6V6's both commonly used 6.6k primary impedance OT's. So chances are the OT will be fine. But it's a good idea to check anyway. Oh... Why would a 4 6V6 OT be Ok for a two 6l6 amp if they both use a similar primary impedance??? Because if you run half the speaker ohmage as a load that would reflect the correct impedance for two bottles instead of four.

To know if the OT is suitable for a pair of 6l6 tubes you need to check the primary impedance. It's not hard to do and requires minimal tech tools.

If the OT has multiple secondary taps you will want to do the test with each of them.

You need a low voltage AC (not DC) signal (like a signal generator or even a keyboard) or power source (like an AC wall wart type transformer) and a way to measure voltages.

Put a low AC voltage across one of the secondaries on the OT. Measure the voltage while it's hooked up and running. if you have multiple secondaries you must re-measure the input voltage for each tap, it will change. When you know the voltage input on the secondary, measure the voltage on the primary. It should be many times the input voltage. Divide the voltage on the primary by the input voltage on the secondary. This will give you the ratio (ie:14:1, 29:1, etc). Let's suppose you get a 29:1 ratio. Square the ratio (29 X 29 = 841) then multiply that with a speaker load. If you multiply by an 8 ohm load you get 6728 (841 X 8 ohms = 6728. This would be your primary impedance. Since 6600 ohms is a common primary for 6l6, and this OT is designed for about 40 watts, it is perfectly suitable for a pair of 6L6 tubes into an 8 ohm speaker load. Now lets say you multiply by 4 ohms (841 X 4 = 3364) This would be a little low for a pair of 6l6 tubes. But about right for four 6l6 tubes. But, you know this OT is designed for about 40 watts so you cant use it for four big bottles. So you would reason that you need an 8 ohm load to run this OT with a pair of 6l6 tubes. There is a little reasoning to do but it's not hard.

Chuck