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I agree that it’s more than a small amount of work to move the pin 6 wire to pin 9, but the only reason the wire is thick is for mechanical convenience during assembly. Use any wire you want, to bridge and bypass the nines, and clip out the wire segments on either side of the sixes. I think I did this on my own 106 years ago, to get access to more spares. And certainly for debug purposes it’s easier to go back to a known-working tube set.

Dave Wise

From: [email protected] <[email protected]> On Behalf Of Albert Otten via groups.io
Sent: Thursday, March 03, 2022 1:05 PM
To: [email protected]
Subject: Re: [TekScopes] Type 106 Saga (Again)

On Thu, Mar 3, 2022 at 05:49 PM, Stephen wrote:

[Albert:]
May I ask again whether or not Vk (= "A") can be varied with the Amplitude
knob to at least -150 V or so?

I don’t think so, but I’ll check again later.

What I can tell you, however, is that when I connect a scope to the Fast-Rise
output, the flat signal (AC coupled) goes down when the intensity knob is
turned up, and up when the intensity knob is turned down…

Stephen, you probably mean the Amplitude knob. The fact that the Amplitude knob still does something in the Fast Rise mode corresponds to what previously has been discussed by you and Dave. You wrote

Meaning that I see that both sides (B side) are always connected no matter the position of the switch.
As if the switch was just there for nothing…. I doubt this is normal, otherwise why even have them
go through a switch in the first place…. Just connect them directly…

This is like the switch remains always in the position as shown in the schematic, that is in the High Ampl position.

Today you wrote

However, what greatly confuses me is that the unit was perfectly working before WITH pin 9 entirely disconnected, and pin 6 connected.
The unit had no modifications whatsoever, as if it were running with 7189A’s without modifications…. I don’t get it.

Actually each pin 9 is connected to GND via a resistor while (with EL84s) all pins 6 are connected and decoupled to GND but otherwise floating (if not connected internally to an electrode). That's why I brought this point up again. You don't know to which DC value the pins 6 drift when loaded by a (10 M input?) DMM.

But I will do the modification before I do anything else.

It's a nasty job to "move" the pin 6 connection to pin 9 for each tube. The pins 6 wire is rather thick, probably with reason. Pins 9 are difficult to access. For the moment I would postpone the modification and use the "original" set of EL84 tubes that worked previously.

Albert