Hot Rod Deluxe reverb tank spec question

[glebert]

Got this HRDlx as a fixer and was told the reverb tank that was in it had been pulled from some Marshall amp. It is a 4BBxxxD tank, once I got the amp working the reverb sounded choked. Every replacement tank I see online is a 4EBxxxB tank, which I had a few spares of. Every 4EB tank I try in it sounds terrible, boomy, etc. The 4BB tank actually sounds great if you get the tank in the correct orientation (vertical mount connectors down, hence the code D). Pretty sure I can't mount the tank in that orientation, so probably need to get a different tank, but want to get the right one.

I know that the original Blues Deluxe amps used a 4BB tank, where the reissues used a 4EB. Supposedly the HRDlx was a replacement for the original Blues Deluxe. Does anyone know if the early HRDlx amps used a 4BB tank like the original Blues Deluxe?

Thanks,
Greg

[Enzo]

Are the drive circuits the same or different? As far as I can see the 4BB circuit drive is identical to the 4EB drive. SO looks like either will function. These circuits are very flexible anyway. If you like the 4BB better, then use it. Doesn't matter what they did or didn;t do in the past.

I am sure Fender had a reason for no longer using the BB pan, but it could simply be a matter of only stocking two types of pan instead of three.

[J M Fahey]

Too busy now to check the Accutronics tables, but one Marshall/Fender difference I expect (and suppose checking those tables will confirm) is that Fender, like most others, uses a single TL072 half to drive its tanks.
Now this is no "power amp", not even "mini" power amp by any degree, and has puny 5mA maximum output current capacity, so Fender in general (always talking SS drive ones, not tube + transformer which is very different) uses the "easiest to drive" tanks, meaning relatively higher input/drive impedance.

While Marshall in the old days for some reason kept using obsolete 1458 Op Amps exclusively for Reverb duty (I *think* Randall or Music Man did the same) which I guess have (undocumented) higher current capability and later switched to using 2 or 3 TL072 (or TL074) sections in parallel.

Which makes no surprise that "Marshall tanks are choked" if driven hard inside a (SS reverb) Fender amp.

But just get what the Fender schematic (or BOM) asks for

[glebert]

Which makes no surprise that "Marshall tanks are choked" if driven hard inside a (SS reverb) Fender amp.

But just get what the Fender schematic (or BOM) asks for

Sorry for not being clear, the reason the 4BB ("Marshall") tank was choked was because it was sitting horizontally in the bottom of the cab when you set it up vertically it sounds great. This makes some sense considering it is a "D" mount unit.

Schematic calls out 4EB tank, which sounds terrible, hence my confusion.

[Tone Meister]

See if these links will help you determine what you need:

https://www.amplifiedparts.com/tech-...d-and-compared
https://www.amplifiedparts.com/tech-...specifications

[g1]

All the HRDlx schems. I have show the 4EB. The blues dlx with 4BB has the same drive IC circuit, but the coupling cap into the IC is slightly different which may affect the boominess (330pF vs 470pF).
The recovery circuits are considerably different.
Like Enzo said, if you prefer the sound of the BB, go with that.

[Enzo]

Recovery circuits differ, but the pans themselves all have a B type output transducer.

[nevetslab]

As I recall, the Deluxe Reverb uses the same tank as the Twin Reverb, which is a 4AB3C1B....A = 8 ohm input, B = 2250 ohm output, 3 = long delay, C = input isolated/output gnd'd, 1 = no lock, B = horizontal open side down. A 4BB tank has 150 ohm input imped and 2250 ohm output imped. It does load the op amp, but does get away with it. I've had to re-position the suspension springs so the tank assembly inside the pan doesn't bottom out if you have one intended for Open side up. Not sure why in some instances, those meant for vertical wall mounting (either connectors up or down) not working when mounted open side up or down horizontally.

[TimmyP1955]

Please let me know if you find any errors:

[glebert]

Had a breakthrough on this problem today. Picked up a Hot Rod Deville 212 the other day, very similar vintage as my HR Deluxe. Has the exact same reverb problem that the HRDlx has. Deville also had an open PI plate resistor. In researching that before repairing it there were some mentions on the web about Fender getting a bad lot of resistors that would open up on the PIs. Thought maybe that if they got some bad resistors on the PI maybe the same supplier sourced other resistors for the rest of the board. Measured the resistors in the reverb drive circuit and R34 is measuring 75 ohm instead of 47 ohm. Piggybacked a 100 ohm on that resistor to test and I no longer have the boomy, eternal reverb that I had before. I wouldn't say that it is my favorite reverb sound in the world, but at least now it is usable.

[g1]

Did the other amp have the same faulty R34?

[glebert]

Did the other amp have the same faulty R34?

The HRDlx R34 measures even higher: 175 ohm

[Enzo]

Just to be sure, reverse your ohm meter leads. measure resistance both ways. A tiny residual charge in the nearby cap can confuse readings.

[glebert]

Just to be sure, reverse your ohm meter leads. measure resistance both ways. A tiny residual charge in the nearby cap can confuse readings.

Did that with the first one, same both ways.

[g1]

Good to know and something to look out for. I wonder if there is something going on with bad connections that could possibly lead to damaged R34 resistor, maybe feedback when tank connection is bad or removed?