The Amp Garage

The LND150 has a maximum Gate-to-Source voltage of +/- 20V. Unlike tube maximum ratings which we routinely exceed, they are serious about the LND150 ratings and the device will fail if you exceed 20Vgs. Heat will also destroy the LND150 in short order. The Reverse Transfer Capacitance is the equival...

palomarsound wrote: ↑Sat Jan 06, 2024 11:43 pm Either side of the primary to ground show full 119vAC. I'm getting 0v across the primary. I do see continuity across the primary.

It's hard to get those results with neutral connected to the primary. Track down the neutral connections.

The Bantam Bass-Amp has a layout that is similar to the Bassman Ten. The Bassman Ten is SS rectified and has a master volume, but the pre-amp is about the same.

It looks as though the OT is connected to ring instead of to tip. If you wired that jack as per Rob's layout, then you have tip and sleeve hooked together and grounded for one OT lead and the other lead connected to ring. The OT secondary would be shorted when a plug is fully inserted. I think I fo...

It looks as though the OT is connected to ring instead of to tip. If you wired that jack as per Rob's layout, then you have tip and sleeve hooked together and grounded for one OT lead and the other lead connected to ring. The OT secondary would be shorted when a plug is fully inserted.

Designing with the 10k pot makes it easy to Keep the total resistance low, as seen by the power tube grids, preventing slightly gassy tubes from thermal runaway. And to make the higher resistance bias circuit even worse, all of the current from all of the power tube grids flows through the bias cir...

Perhaps my problem has more to do with tube variability than anything else. I recently built an amp for a guy that was supplying his own tubes. I built it at my shop, tested and configured with a set of JJ 6L6GCs for an optimal bias setting at 40mA (60% dissipation) +/- 7mA (50% - 70%). I shipped i...

Dr Tony Balls wrote: ↑Tue Oct 31, 2023 2:30 pm Well, do you care to share how to extend range with a 10K pot?

Make the other resistors smaller.

What are people here using for bias pots? I've been using the CTS screwdriver-adjustable ones but they only come in 10K and I find that range a bit limiting. Does anyone have a favorite bias pot option they're using? I like to have things externally adjustable so panel-mount is key. The range is us...

if I turn the intensity control to zero, will the preamp bias on the vibrato channel be the same as if it wasn't connected at all? wondering how the trem circuit would effect the tone on the vibrato channel vs not connected at all (in other words, if the intensity control is set to zero, it's not e...

As for powering the trem circuit, if I connect it to the B node and I'm getting say 460v there, is this acceptable? Vibrochamp schem notes 360v powering the trem circuit. The absolute maximum anode voltage for a 12AX7 is 550V. The Fender AB763 Super Reverb put 460V on the tremolo circuit. The AB764...

If you turn the Vibro Champ tremolo off with the foot switch and turn the Intensity control up, it fouls-up the bias on the pre-amp tube which causes distortion reminiscent of Clapton's tone on certain recordings. If you don't like this distortion, and I don't, you can minimize it by wiring the foot...

The way you have it drawn will put tremolo on both channels because the cathodes of V1B and V2B are connected. If you only want tremolo on the Vibrato channel, then you need to separate the cathodes. Deluxe Reverb Preamp Trem 1.png The tremolo is ahead of the reverb which may or may not be desirable...

So is the capacitor at the input before the diode the only difference between the bias supply for CT vs. no-CT PT use, or is there more going on to it than that? The Ampeg bias supply that you found on Rob's site is radically different than the typical bias supply found with a conventional, non-FWB...

The RC high pass filter component values before the bias rectifier largely determine the rectified V DC at the bias reservoir cap. Such that if more voltage is required, the R or the C or both values could be increased. Increasing the value of C will increase the Vdc at the bias reservoir capacitor...