Can I run 4 ohms into 8 ohm speakers?

Hello, I went to EAR 890's as mono blocks. Set up as directed by EAR. I have Tyler Acoustic custom built 8 ohm speakers with 500 watt powered subs. When connecting to the EAR on the 8 ohm taps I effectively reduce it to 4 ohms. Since that time, I have blown 3 tubes total and took out one resistor. The problem has occurred on both amps. All tubes were new. The last incident occurred within 5 minutes of powering up! Has this been caused by the ohm issue? The tubes blew with great flare! Have I made the classic audioholic mistake of one tweak too many? Please don't chime in about "do you need this?" Looking for answers to the problem. Help me to understand ohms and mono blocking better!!
Thanks so far for the responses. FYI. The subs are connected via line out 2 on the preamp. Line out 1 goes to the 890's. Then 890 out to the monitors.
Almarg, from EAR:

1.Stereo/Mono switch to Mono
2.Connect one channel of the preamp main out to the 890's
Left channel input Only.
3.Connect the "hot" speaker lead to the left channel's output and the ground lead to the ground. Then, using a high-quality cable, connect the right channel's output to the left channel's corresponding output.

Thanks for the help/comments

Is this a miss type or are you saying that you are connecting the amps right and left channel outputs together?
OK, so it appears that we can most likely eliminate the subs as having anything to do with the problem, unless something really subtle is going on.

And it appears that the amp channels are being paralleled, not bridged. That can be done with some tube amps, although not without some risk.

So if I understand correctly you are connecting the positive terminal of the speaker to the 8 ohm tap of one amplifier channel, and you are also connecting that 8 ohm tap to the 8 ohm tap of the other amplifier channel. And you are connecting the negative terminal of the speaker to the common/negative/probably black terminal of one of the amp channels. You are connecting nothing to the common/negative/probably black terminal of the other channel. And by setting the stereo/mono switch to mono and just connecting an input to the left channel you are presumably causing the same signal to be processed through both channels.

Here are the thoughts that occur to me:

1)I'm assuming from the instructions you quoted that the common/negative/black terminals of the two channels are connected together internally in the amp, and an external connection is therefore not needed. But I wonder a little about that. If you have a multimeter I'd suggest verifying that a dead short (zero ohms) exists between the two common terminals.

2)To realize the power increase that paralleling the channels can provide, you should be using the 16 ohm taps for an 8 ohm speaker, not the 8 ohm taps. But I don't think that using the 8 ohm taps instead would in itself cause any damage, and it might even sound better as long as the amp's power capability is not exceeded.

3)What might cause the problems you have experienced, it seems to me, is if anything were to cause one of the two amp channels to "try" to put out a substantially different signal than the other channel. That might result from:

(a)Not setting the stereo/mono switch to mono.
(b)Having a small signal tube in one channel that is weak or dead.
(c)Having tubes in the two channels that are significantly different in their characteristics.

Not sure what else to suggest at this point.

-- Al