Holland Amp: On board reverb drives a speaker directly?

[mike_mccue]

Hi,
A musician dropped off a Holland Amp today that is making a lot of "static" or noise.

This particular amp was custom built for the musician back in the 1990's and so I don't have a model name. It seems like a 2 x 10 hybrid of Holland's 4x10 bassman circuit. One aspect of the design that I am unfamiliar with is the inclusion of a reverb unit that is mounted in the bottom of the cabinet. It has two tubes, two transformers, and a potentiometer.

Searching around last night I saw some photos of Holland 4x10 designs that seemed to use the same unit. I also learned that finding specific info about Holland amps is difficult.

The reverb has two sets of leads coming from the main power supply for B+ and Heater voltage. It has a audio cable with a RCA type connector. Finally it has a direct connection to one of the 10" inch speakers coming from an on board output transformer. In other words the amp looks like a 2x10, but one speakers is for primary sound and the second is dedicated to the reverb.

I pulled the preamp tubes in the main chassis and the "static" noise didn't subside very much, so I replaced them.

I pulled the tubes from the reverb unit and the noise went away... so I guess I need to learn about that unit's design. I don't even know what the power tube is, it is old stock and has blackened glass. The preamp tube looks like an unmarked 12A??.

Does anyone have any info about this Holland reverb unit's design? If I can't find any info I'll pull it and draw up a schematic, but I figured I'd ask here first.


Thank You.

[Leo_Gnardo]

No Holland schemo, but I have seen this sort of thing in early 60's Sano and Ampeg (B-12-X) amps, the diff being their reverb amp is built on the same chassis, not separate, no big deal. The reverb springs are driven by the main amp with a resistor limiting current to them from speaker out, and return/volume brought thru a little Champ-like amp driving a separate speaker. So think simple, the reverb amp is likely no more complicated than that.

Check pin assignments on the reverb amp's power tube. Unless Holland did something very unusual like use a 7591, it's likely a 6V6 or 6L6. Skinny 9-pin? Probably EL84. Pre /drive tube, after checking in assignments agan, try 12AT7 and 12AX7 if the pins look to be standard 12An style wiring.

[J M Fahey]

This Retro craze has to stop someday [tm]

Please confirm that that particular 10" is connected to that small transformer out in the subchassis and anything else.
Meaning only 1 pair of wires going from it to the OT.

If so, yes, it uses the obsolete (even when it was originally used 60 years ago) technology of driving an extra amp and speaker just with the reverb signal.

Which, among other problems, means that you lose 1 speaker and the power driving it if you choose not to use reverb, that you don't have reverb on the other speaker(s) , that you may have phasing problems between speakers, etc.
Oh well.

The other possibility which I'd like to discard is that the main amp drives both speakers, and part of that signal tapped from a speaker drives the reverb tank directly, whose output goes back into a semi conventional reverb circuit.
In that case that speaker would have a couple wires reaching it from the main OT and another pair joining it to the reverb tank.

OK, googled a little and found a reference to:

the one with the seperate 10" wet speaker as well.

which looks like what you have.

In that case, no big mystery: some preamp signal goes to a little power amp (6W?) passing first through the reverb tank.
Or, the reverb tank is driven directly by a tap from the main power amp, its output feeding the secondary amp.

What does the main amp use?

If confined to a single, vintage type 10" speaker it can't have much power either.

Rich kid's bedroom amp.

Your "blackened" tube might be an old 6V6 or at most a similar age 6L6 , please post some pictures.

As of troubleshooting the noise (please describe it better), check that auxiliary amp like any small tube amp, the reverb tank and cables and connectors involved ... there's nothing else there.

EDIT: ouch !!! simulpost !!!!
Wanted to add that Leo solved the Reverb problem in a MUCH better way

[Leo_Gnardo]

Good morning Juan! I was going to mention the Ampeg Echo Twin too. Has two identical power amps, and a toggle switch lets you decide both handling the same signal, or dry to one side, reverb only to the other. Ampeg weren't much worried about one speaker's effect on the other with only @ 12W to each. A terrific and very underappreciated amp that has shown up on at least one multimillion-selling recording. Somebody's trying to sell a wrecked one locally here for a mere pittance only $800.

[mike_mccue]

No Holland schemo, but I have seen this sort of thing in early 60's Sano and Ampeg (B-12-X) amps, the diff being their reverb amp is built on the same chassis, not separate, no big deal. The reverb springs are driven by the main amp with a resistor limiting current to them from speaker out, and return/volume brought thru a little Champ-like amp driving a separate speaker. So think simple, the reverb amp is likely no more complicated than that.

Check pin assignments on the reverb amp's power tube. Unless Holland did something very unusual like use a 7591, it's likely a 6V6 or 6L6. Skinny 9-pin? Probably EL84. Pre /drive tube, after checking in assignments agan, try 12AT7 and 12AX7 if the pins look to be standard 12An style wiring.

Thanks very much, the description of the layout is very helpful and seems to match what I am looking it. This will get me started.

[mike_mccue]

Thanks for the info.

[Jazz P Bass]

Interesting how they drive a separate reverb speaker.
Here is the Ampeg B12 X schematic (thanks for the tip Leo).