Ampeg V4.com

forum

You are not logged in.

#1 2011-01-28 13:26:05

Liquids
Member
From: CT
Registered: 2010-08-01
Posts: 491

Output Transformer Replacement

No, my output transformer  is fine.  For better or worse.

My question/thought is, for those of you that prefer V2 output to V4 - and hesitate to pull the trigger accordingly - why not consider making your V4's output transformer a V2 from fliptops?

I mean, I realize that most people just pull two tubes.  I'm not so into that.  I like the impedances to be as stated and 2 ohms is more useful to me than 16 ohms.

Also, the transformer's primary is expecting to 'see' a certain load from the tubes, like a speaker is, correct?

For example, on my SE silverface champ, I have a replacement transformer (makes it sound SO much better) that has 7k and 5k taps. 7k for 1x6v6, 5k is for running a 6L6GC.

Likewise, and possibly more critical in certain cases, the amount of tubes that the power transformer is expecting you to run impacts what impedance the primary is designed for, no?

Anyhow, all that to say, I think if people are interested in running only 2 power tubes in their V4 - like V2s  which are harder to come by - why not consider a drop in a replacement V2 output transformer? 

I think if mine were to blow, I'd do that, thought mostly because I'm anal ANd cheap, and I don't like having to buy quads when it's only a notch more clean volume (that I don't need) over a pair.  Actually, with the going cost of the winged C tubes, when I blow through my current quad and cheapo backup quad, the next time I re-tube (hopefully years from now) it might be only negligibly higher cost to buy the $130 V2 transformer and a pair, rather than a quad, since I could do the work myself. 

Are their sizing issues?

Just a thought for discussion.

Last edited by Liquids (2011-01-28 13:29:58)


Matthew

Offline

 

#2 2011-01-28 17:10:16

hangman
Banned
From: Seattle Washington
Registered: 2006-09-04
Posts: 1848

Re: Output Transformer Replacement

the transformers are different sizes...  so that would be an issue.   
V2s really aren't too hard to come by.  VT40s are all over.
I think the 2 tube solution or a hot plate are more elegant solutions to keeping the volume down.

in regards to the primary impedance,  you have to keep in mind that transformers do not have an impedance so to speak... they reflect impedance.  so with your champ transformer,  the primary is 7k for 6v6... but only with an 8 ohm speaker.  change the speaker, and the reflected impedance changes too. (this is the same reason you have to change the impedance switch when pulling two tubes)

Offline

 

#3 2011-01-28 19:24:18

rob
Member
Registered: 2008-10-28
Posts: 171

Re: Output Transformer Replacement

Yes,there would be no advantage to fitting a V2 OT. In the case of the Champ, it is a major upgrade though. The larger OT for the Champ really increases bass response. For the V4, running only 2 tubes gives you a wider margin of safety as it is designed to take twice the primary current as what it sees with only 2 tubes. Running two output tubes, it would be very difficult to blow the V4 OT under normal operating conditions.

Offline

 

#4 2011-01-28 19:33:33

Liquids
Member
From: CT
Registered: 2010-08-01
Posts: 491

Re: Output Transformer Replacement

FYI, my previous assumption is that it's not optimal for the V4 transformer to see 2 tubes rather than 4 - not necessarily dangerous, just not optimal. Guess that's not the case. But there's a lot I don't understand. 

But on the other hand, it's the same as running a 4xEL34 Marshall with just 2xEl34, or a Twin with 2x6L6GCs - which I would think would be more common if it were not a compromise somehow, no?

Last edited by Liquids (2011-01-28 19:35:26)


Matthew

Offline

 

#5 2011-01-29 05:52:10

hangman
Banned
From: Seattle Washington
Registered: 2006-09-04
Posts: 1848

Re: Output Transformer Replacement

you can do this with many marshalls, and it is fine, (assuming you switch the impedance)  the twin on the other hand has a Single Secondary,  so you can't switch to a different secondary and reflect back the correct impedance.

i forget the actual impedance that the V4 is setup for,  but lets say that ampegs engineers wanted the plates of the power amp to see 3.6k as their load.   

3600 = (turns ratio)^2 * load impedance.

so for the v4:

turns ratio for 8ohms is sqrt(3600/8) =21.21
Turns ratio for 4 ohms is sqrt(3600/4)=30
turns ratio for 2 ohms is sqrt(3600/2)=42.43

with four tubes in the amp you have two pairs of tubes in parallel.  which means each tube is seeing a portion of the load.

when you remove two tubes,  the output impedance doubles.

so 2 tubes really want to see something more like 7.2k

so if you have a VT22 like I do, and the load is 4 ohms,  i switch the switch to 2. 
and using the figures from above...

For the 2 ohm setting the turns ratio is 42.3

42.3^2=> 1800*4(our speaker load) =7200 
which is exactly what we want. 

This practice is relatively common,  i think the reason so few people do it is due to two reasons.
1. People don't want to mess with their amp... they convince themselves that it could blow up their amp. which is quite possible if they go the wrong way.
2. techs tend to not recommend this method to people because they don't want to be held accountable if the person makes a mistake and blows up the amp.

Offline

 

#6 2012-11-05 23:27:06

Liquids
Member
From: CT
Registered: 2010-08-01
Posts: 491

Re: Output Transformer Replacement

Anyone know the specs for the output transformer on their V-series amp, of any ilk?


Matthew

Offline

 

#7 2012-12-26 16:17:45

Liquids
Member
From: CT
Registered: 2010-08-01
Posts: 491

Re: Output Transformer Replacement

Well, to answer my question, and FYI, as a follow up - on the V4(b) I tested, the primary impedance measured/reflected ~3k (just shy of 3k to negligible but slightly varying degrees depending upon the tap and/or the line voltage at the moment). 

I did this via powering the OT  per procedures that involve putting an AC voltage on the primary/secondary (one of the two, at a time, and done correctly), measuring the voltage on the 'other' side of the transformer, and then using those numbers to calculate impedance, in reference to which secondary 'tap' is being used/measured.

This article was a big help, and I can't find it, but there was info I believe I got at GEOFEX that also assisted to fill in the gaps:

http://www.radioremembered.org/outimp.htm

I cannot assume that the V2 OT's reflect a 6k output impedance, but it seems likely...however, they run a higher voltage, so some level of change on the OT impedance as compare to the V4 may have been a sensible design change.  I do not have a V2, so I cannot test it.  I also only measured the OT (and PT) of one of the two V4(b) I have available to me.

Last edited by Liquids (2012-12-26 16:20:01)


Matthew

Offline

 

#8 2012-12-26 22:59:40

hangman
Banned
From: Seattle Washington
Registered: 2006-09-04
Posts: 1848

Re: Output Transformer Replacement

Thanks Matthew!  Do you mind if I update the transformer spec sticky and credit you/ this thread?

Offline

 

#9 2012-12-27 09:34:26

Liquids
Member
From: CT
Registered: 2010-08-01
Posts: 491

Re: Output Transformer Replacement

No credit necessary (just liability), but feel free.


Matthew

Offline

 

Board footer

Powered by PunBB
© Copyright 2002–2005 Rickard Andersson