6AQ5 amp project

[beatnik]

Hi everybody,

I have some parts laying around and have been thinking of building a guitar amp based on 6AQ5 power tubes.

The output transformer is a Stancor A-3852 which is rated at 40 DCmA / 18W

I am wondering if this output transformer would be suitable for a power amp with 4x 6AQ5 tubes.

I have tried understanding the total output current using this calculator https://robrobinette.com/Tube_Bias_Calculator.htm

If the value of 300V for plate-to-cathode voltage is used, that puts the total current in the ballpark, 40mA max safe dissipation / 38mA average / 34mA cool

The datasheets I have seen have maximum plate voltage rating at 250/275V. That would mean is impossible to obtain the 300V plate-to-cathode voltage ?

My theory knowledge is quite limited, so I am trying to understand what I should keep in mind, hopefully this will be a chance to understand more about tube amp design.

Any suggestion would be highly appreciated.

[Dave H]

The output transformer is a Stancor A-3852 which is rated at 40 DCmA / 18W

I am wondering if this output transformer would be suitable for a power amp with 4x 6AQ5 tubes.

I think that OT would be more suitable for 2 x 6AQ5. It's rated at 40mA per side. The calculator is for 2 tubes. The current for 4 tubes would be double.

[mozz]

Yes, 2 tubes would be more like it. I think that transformer has a bunch of output taps so you can get a lot of primary choices. 4 tubes will give you about 18-20 watts max, i don't know why the transformer is rated at only 40ma but maybe it was a replacement for something running higher voltages and less current.

I have a quad 6aq5, running a little under 300v if i remember correctly. The output transformer i used was a old PA amp which had a quad of 6v6 so it fit the bill pretty good.

A pair of 6gk6 will get a little more wattage than 6aq5 and handle 330v if available.

[beatnik]

Thanks for clarifying

I am currently digging for some schematics I can take inspiration from

[Joeboo]

Hi: i recently built a 2x6aq5/el90 super lead and this amp is my favorite.
the schematic an build thread I used for my build is from:

https://ampgarage.com/forum/viewtopic.php?f=9&t=27104

here is mine:


I loved that amp so much I just completed a 4x6aq5 with a Hammond 275 0 275 - a big diode to get the voltage down to around 300 on the plates and an Edcor 5.2k 30 watt OT.... it sounds different than my little 15 watter. These tubes are really nice.

Hope this helps... Joe

PS: On my build I had to put the presence pot on the back of the chassis.