72 Quad Reverb "no reverb"

[Mars-Hall]

The symptoms are no reverb, however the reverb knob does affect the tone of the amp.  It increases treble as you turn it up, until 7 or 8 then it causes feedback and distorts any notes played, in a bad way.  Also, the springs can be heard when the tank is knocked.
 
Here's what I've checked so far:
Replace the driver and pick up tubes with known good.
Checked the return and send wires for continuity.
Check the tank transducers for continuity.
 
I do plan on changing the 25uf/25v electrolytics on the board.  Could a dried cap cause this issue?

[Mars-Hall]

Since my first post, I've managed to prove out the reverb tank.  I replaced the electrolytic caps on the board.  With known good tubes, I get no voltage pins 1 or 8 of v3 and voltages "in range" on pins 1, 3, and 6 of v4.  From what I can tell there seems to be no burnt resistors on the board.  Do I look to replace the reverb transformer?

[PRR]

There seem to be several "Quad Reverbs". I don't remember 1972, or which ones were sold then. I hope I am looking at a relevant schematic.

> no voltage pins 1 or 8 of v3

When you turn-up Reverb knob, and kick the amp, do you hear thunder?

If so, power-down, disconnect the Blu and Red on the reverb transformer, measure the Ohms across that winding. (With some meters, you may need to short the Grn Blk winding to get a good reading.) Several K-Ohms is reasonable. Meg-Ohms or Overload (no connection) is bad.

[Mars-Hall]

I get no reading at all across the the blue and red wires of the reverb transformer.

[eleventeen]

If you are saying there is infinite resistance (eg; open ckt) across the blue-red of the rev tranny it is toast. A bit rare but not unheard of.

[Mars-Hall]

What I mean to say is, the meter reads as if I weren't testing at all.  The meter reads the same if I add or remove the leads.
 

[sluckey]

The primary of the reverb transformer is open. You need a new one. Hoffman sells them right here.

[Mars-Hall]

The primary of the reverb transformer is open. You need a new one. Hoffman sells them right here.

Thank you sluckey.  I will source the part from the store here.