Ampeg V4.com

Good question.  What resistors in the power section blew out of curiosity?

All those 5 watt wirewound can be mounted right to the tube pins, and often are on other amps.  Plenty of pictures to be had on this very website, if you go to google.com and type (or cut and paste) this:

site:ampegv4.com   

Then, choose 'images' it will show you a lot of the images that have been posted on this board.  You can also surf posts in the workshop section, this stuff is discussed from time to time.

Last edited by Liquids (2012-02-08 01:07:38)

A thought regarding pulling two power tubes - which I do with my V4.
It affects the output transformer impedance...

If the 8 ohm tap effectively becomes a 16 ohm tap when two power tubes are pulled - following, if one want's to maintain the amp's negative feedback as designed - shouldn't the feedback tap be moved from the 8 ohm tap to the 4 ohm tap, since the 4 ohm tap is now functioning as an 8 ohm tap?

I've got a great idea!  I could drill a hole, and put in a switch that either parallels a resistor in the feedback loop, or switches the stock feedback tap between the '4 and 8 ohm taps' as labeled, so it can be switched on the fly depending on how many tubes I run!!!   

I was thinking a little more and thought that I might add switches and two holes so that both options would be available to me...

I hope you know I am kidding, strictly to tease you.  I was awaiting a comment about a mesa/boogie! 

On a more serious note - I actually had my amp on the bench tonight...it's been a while.

I switched the transformer tap since I have no reason to use the amp with 4 tubes.  60 or whatever watts I get clean has always been enough. I'd rather eat/blow 2 tubes at a time, thank you.   

But I've been thinking and looking.  The KT88s fit in the V2 nicely, because they look to effectively only utilize the 2 'spots' for power tubes away from the transformer, as compared to a V4.

Typically, tube pairs are inner/outer, or power tubes 2&3 are a pair, 1&4 are a pair, if you follow.
I swapped the wires that feed pins 3/4/5 of tube sockets 1&3. Now, tube pairs are 1&2, 3&4.

I am thinking that now  I can more easily run 2 large bottle tubes like KT88s.  Again, I only need 2.  These can go in the now-paired power tube sockets away from the transformer, and I can re-install spring clamps for those sockets permanently.  I can run a pair of 6L6GCs like I have now in slows 1&2 right next to the transformer, and keep the bear clamps for those two sockets since they fit just fine.

Lastly, I may be able to make use of the standby switch as a way to parallel a resistor in order to bias for either 6L6GC pair or KT88 pair as desired.  No irreversable mods, and everything was marked with p-touch labels so I don't forget.

I had a quad of 6550s in there at some point that I eventually sent back, so I'm all but certain I'll have no issue with running KT88s in the 'far' sockets away from the transformers.

Lastly, this also gives an option to choose EL34/6CA7s instead of KT88s and re-wire those sockets as needed, if I ever wanted to.  All reversable...not that I'm anticipating selling the amp, especially now!

Last edited by Liquids (2012-10-09 04:28:16)