Problem with deluxe reverb clone

[rutledj]

I built a deluxe reverb clone using hoffman amps layout and deluxe speced transformers.

It sound great but it does not have any breakup until the highest volumes. I thought it was typical for breakup to occur around 4 on the volume knob.

The voltage levels seem a bit high on the preamp tubes (around 230v). Do I need to drop that more?

Thanks,
Rut

[martin manning]

That's a good place to start, seeing you're 50V high. Are all of the voltages over the expected DR values?

[rutledj]

The PI and power tubes on spot on. Just the preamp tubes are high. Need a higher dropping resistor in the B+ line maybe?

[tele_player]

The PI and power tubes on spot on. Just the preamp tubes are high. Need a higher dropping resistor in the B+ line maybe?

That's what it'd do, assuming plate and cathode resistors are correct on preamp tubes.

Robert

[martin manning]

Is this is a complete DR circuit with reverb and tremolo? Both channels fully functional?

[mandopicker]

If the tubes are not new, try plugging in a new PI 12AT7. Perhaps the most important and hardest working tube in the amp.

Also, the voltages at the preamp would not necessarily make me consider it a cause for limited breakup until the higher dial readings. Is the amp loud otherwise?

[tele_player]

The PI and power tubes on spot on. Just the preamp tubes are high. Need a higher dropping resistor in the B+ line maybe?

I'm curious - what it's your reference - the original Fender schematic?

[slider313]

The Hoffman layout uses 1K and 4.7K dropping resistors. Go with the original Fender AB763 values of 10K and 10K

[pdf64]

In what sense may the PI be seen to be the hardest working tube in a DR?

It sound great but it does not have any breakup until the highest volumes. I thought it was typical for breakup to occur around 4 on the volume knob.

The particular rotational setting to achieve the gain required to overdrive the amp will be greatly affected by the tone control settings and the taper of the volume control. As well as the output of the instrument being used.
I think that the standard Fender volume control taper is 30%, both in the original BF era and for the RI, see the 1M30A spec on http://support.fender.com/schematics/gu ... ematic.pdf

My hunch is that your amp has a standard 10 or 15% taper volume pot fitted?
To confirm, isolate the pot and measure the resistances either side of the wiper with it set halfway.

[xtian]

The particular rotational setting...

That's a very nice way of saying, turn the knob until it sounds like you want. Can't get it to sound like you want? Then there's something to work on.

[wyatt]

The Hoffman layout uses 1K and 4.7K dropping resistors. Go with the original Fender AB763 values of 10K and 10K

That would do it.

The "large" BF reverb combos...Pro, Super, Twin, etc. all had the 1K/4.7K resistors.

The "small" Fender combos, Deluxe and Vibrolux had the 10K/10K resistors.

It makes a big difference in preamp headroom and why the big amps can stay so clean.