Built a 5f4 Tweed Super but have low distorted volume!

[hamilcaster]

Hello! Today, I replaced the old bias supply circuit and now have rock stable negative voltage and tube bias, though I need to alter some component because I max out at about 35mA current.

I also added in a bucking transformer to the AC mains and made it switchable from 0/-6/-12 volts mode. Now my B+ is down around 430vdc, only 15 volts above the schematic and I am ok with that! My heater voltages are much closer too.

The output is still quieter than I'd imagine it should be. I can sit in front of the amp and crank it without cause "too much" pain. Either my hearing is worse than I thought or something's up still. I overdrives into a sweet marshall-esque grind at full volume. I'm thinking my OT may not be ideal for this application since I have no idea what it used to drive in its former circuit. All I know is that it was from a Baldwin organ. I'll apply a small AC voltage across the primary and measure what I get on the output. Given 4 ohm load, I should be able to calculate what the tubes are seeing. I'll report back with some more information as soon as I get a chance. Stay tuned! I am quite thrilled!

[hamilcaster]

Well there you have it: I put 7.1VAC across the primary of the OT and measured 0.315VAC on the secondary. Doing the math: this ratio turns out to be 22.5:1. Squaring that 22.5^2 x 4ohm = 2,025 ohms! I believe I am looking for a primary reflection of 6k, according to new transformers sold for this amp. I guess that would explain why the amp has a lower output. I'm thinking my 4ohm speaker load is connected to an 8ohm secondary tap (the one and only), which would bring this OT to about 4k and that sounds common for 6l6's. Do you think I should just find a new OT? Was hoping to use salvaged parts for peace of mind but if I'm abusing my output tubes, I don't mind getting another one.

[g1]

I'm thinking my 4ohm speaker load is connected to an 8ohm secondary tap (the one and only), which would bring this OT to about 4k and that sounds common for 6l6's.

I think the opposite is true, if you want to reflect back a higher impedance to the tubes, you need to run the secondary into a higher impedance, not lower.
So if it is 2K primary, and secondary is an 8 ohm tap, you want to run into a 16 ohm load to make the primary 4K.
Try running into 4, 8, and 16 ohm load resistors and measure power out. You may find something useable.

[hamilcaster]

I think the opposite is true, if you want to reflect back a higher impedance to the tubes, you need to run the secondary into a higher impedance, not lower.
So if it is 2K primary, and secondary is an 8 ohm tap, you want to run into a 16 ohm load to make the primary 4K.
Try running into 4, 8, and 16 ohm load resistors and measure power out. You may find something useable.

Ah yes. Assuming the tap is an 8ohm, the formula I was using wouldn't be correct since I'm already mismatching the load to the secondary. So If I ran the speakers in series I could also measure and see what the results were (without going to the store to look for power resistors). Even if I got closer, there's not much I could use if I have the speakers I'm going to use and likely don't want to run them in series (besides safety, I always thought parallel was the better sounding option).

[g1]

Let your ears tell you the better sounding option .

[hamilcaster]

Let your ears tell you the better sounding option .

Ok, speakers in series I got about 28vac max on the output! That's all I'll ever get from this thing and it sounds great!

Just realized that in series the load is 16R. 28^2 / 16 is 49 watts! Two 20-watt speakers in series only have a rating of 25 watts right? Yikes!

Edit: apparently series/parallel doesn't effect power handling so I think I'm ok but they would be at the edge if their handling with 50 watts of speaker and practically 50 watts of amp power. Not super ideal.