Over-Sizing Power Transformers - How much is too much?

[rocketeer]

Please welcome me to your humble board. I have lurked and learned much for a long time and now feel like I'd like to get on board.

I've been a long time builder and designer. I've used my own designed and built stereo amp head professionally for 15 years and then I switched to a DIEZEL VH4S stereo head for three years and am now back to my head. (I was missing my tone stacks). My head is a three channel high gain design however it was built with dual 6V6 PP outputs. After using the Diezel and learning a bit internally why his amps sound the way they do I've recognized that I need to take my amp up to dual 6L6 or EL34 outputs. Diezels use VERY high feedback in the output section making the amp react fast and making it very articulate (I like). Distortion is almost exclusively derived in the preamp sections (again I like). Supply filtering in the amp is also pretty high adding to the extended low end in these amps (as well as an active tube EQ 80hz bump). My question is in the rebuild of my amp how much is too much in the need of current rating of the power transformer? A Hammond 290FX (Fender Twin) transformer has 517ma; Yet a 290HX (JCM800) xformer has only 420ma of listed current. I want to stay on track with a very tight power supply with little or no sag in HT voltage. I'm not stuck on using traditional replacement transformers either. Going oversize is fine with me.

[jaysg]

You said 2x 6L6GC or EL-34? Either would be fine. They're both for 100W+. In an amp like that, I would think that extra capacity on the heaters would help keep the whole thing cool and reliable...maybe 2A extra.

[Structo]

For a reference the Fender Twin Reverb PT has 450ma.

So if your tube load is similar that should be enough.

Check out Magnetic Components for transformers.

http://www.magneticcomponents.net/

[Colossal]

Please welcome me to your humble board. I have lurked and learned much for a long time and now feel like I'd like to get on board.

I've been a long time builder and designer. I've used my own designed and built stereo amp head professionally for 15 years and then I switched to a DIEZEL VH4S stereo head for three years and am now back to my head. (I was missing my tone stacks). My head is a three channel high gain design however it was built with dual 6V6 PP outputs. After using the Diezel and learning a bit internally why his amps sound the way they do I've recognized that I need to take my amp up to dual 6L6 or EL34 outputs. Diezels use VERY high feedback in the output section making the amp react fast and making it very articulate (I like). Distortion is almost exclusively derived in the preamp sections (again I like). Supply filtering in the amp is also pretty high adding to the extended low end in these amps (as well as an active tube EQ 80hz bump). My question is in the rebuild of my amp how much is too much in the need of current rating of the power transformer? A Hammond 290FX (Fender Twin) transformer has 517ma; Yet a 290HX (JCM800) xformer has only 420ma of listed current. I want to stay on track with a very tight power supply with little or no sag in HT voltage. I'm not stuck on using traditional replacement transformers either. Going oversize is fine with me.

Rocketeer,

Welcome dude! Sounds like you are doing some very cool work. I love the high gain Diezel sound and am a huge fan of Adam Jones' work with Tool. He combines a 100W Superbass (converted to Superlead specs), channel 3 on a Diezel VH4, and either a Dual Rectifier or I think more recently, another Diezel. This yields the most bone-crushing grind. The Superbass/lead covers the mid-range frequencies well and the Diezels get the low end.

I would be really interested to hear more about your investigation into the Diezel sound (and specifically what makes those amps tick). I read that there is some cool tone shaping going on in the circuit and carefully controlled highs. Your observations of the tight, extended low end in those amps is right on with what I've seen and heard. I have a schematic of the VH4 and a few studies of specific parts of it, but nothing comprehensive showing all values. Some interesting things going on though.

[rocketeer]

Thanks for the welcome.

Colossal Ch3 on the Diezel is a work of art.

In my amp Ch1 is pristine Fender sounding, Ch2 is like a somewhere between a reworked Fender and Marshal 800 sound with wonderful controllable crunch. My Ch3 is like the VH4 ch 3 and I also have an added gain push for my Ch3 that gets into just the right amount of compression for lead playing. All three have independent tone stacks. In high gain amps blocking distortion is your enemy and you have to get a good balance between tone shaping ahead of the grid stopper resistors in each gain stage of the preamp .... at least that's my take.

I have drawn the VH4S output section and that is the key to its tight fast sound. Lots of feedback to the PS. The only unknown to me was what current ratings were on the PT. The OT's where 3.4k just like 50 watt Marshalls but I'm looking forward to trying up around 6k too.

Thanks for the input. Does anybody know the real world full power current draw of both a 6L6 PP or EL34 PP (50 watts) (running around 450 volts)?
I know both of the PT's I mentioned are for 100 watt amps so building a stereo 50watt per channel amp they should work fine. I also know that the amp manufacturers are notorious for cutting corners and putting in PT's that barely meet specs.

[tubeswell]

An over-spec'd PT is better than an under-spec'd one IMO. You don't get that much sag from an under-spec'd PT that its worth the difference/compromise in reliability.

(And if you're talking 'euro' voltage PTs, they have to be physically bigger to cope with the inductance at 50Hz, otherwise they just end up cooked in next to no time at all.)

[guitarmike2107]

The Hammond trannies your looking at are for 100watt amps, i.e. 4 x 6l6 or 4 x EL34. if you build a 2 x 6l6/EL34 with those trannies is should be plenty power for what you are after.

is it too much.. well it will help make it very stiff which is what you are after, so no... but it will be heavier.

[kg6epv]

Bigger is better. You want a robust power (and output) section. It is true that some amp manufacturers spec trannies that can barely handle the job... it is sad when bean counters call the shots. For a little more money you can have transformers that easily handle the job, sound amazing, and will last a lifetime.
Often I have heard folks on these forums say that the OT is important and the PT is not. Not true... you will lose bottom end and response time with a barely adequate PT. Of course the OT is very important also... the OT makes more difference to the tone than any other single component. But changing to a better power transformer can really change the feel of an amp.
I have been building transformers for Tube Amps all my life, but you needn't take my word for it... check out page 199 of Gerald Weber's book, "All About Vacuum Tube Guitar Amplifiers".
I hope this helps! Bob Wood, Transformer Design and Supply, San Jacinto, CA
www.transformerdesignandsupply.com

[Structo]

Hi Bob,
I was checking out your website.
Are you going to limit your transformers to Matchless amps or will you have other offerings?

[kg6epv]

Hi Tom! We make them for all kinds of amps, and of course, Matchless as well. We have our own 5E3 Tweed set, an 18W Marshall set, a JTM45, Plexi, etc, etc. All are our own designs and they are an upgrade to the originals. We can also design and build most anything you could think of. We are looking to expand our product line all the time... we are working on a new website as well, it will have much more info and all.
Usually we offer a sweet deal on a new design, because it takes 1-2 weeks to get it out, and we ask for honest feedback in return for a great price. So far everyone loves all the new models and come back for more, we just want to be sure they are top notch in every way, and everyone is happy. We stand behind all we build, and we design and build them all to last a lifetime.
Our engineer, my Dad, has been designing transformers for over 50 years now, and he is amazing. As an Amateur Radio operator and an amateur amp builder myself, i can relate to anyone who wants to build their own. I like to think in some small way i am helping to make good music. I am sure not doing it with my guitar playing, lol. But I keep trying.
If i can help anyone with transformers, feel free to drop me a line. I am a paraplegic and I do this mostly for fun, but I will be a transformer man for life... i love my job. I get to make people happy!
All the best fellow amp lovers! Bob, TDS
www.transformerdesignandsupply.com

[M Fowler]

Bob I can vouch for your transformers. That 18w Marshall set you made for me was excellent.

I like the fact you went with 140mA instead of the 120mA commonly found. High quality construction and tone.

Mark

[kg6epv]

Thank you Mark! We really try and build the best while keeping them affordable. Thanks for the feedback!!! Bob

[Colossal]

Bob,

Great to hear that you love your work and do what you love. That is great this day and age and most aren't so lucky. Say, do you build transformers for West Labs by any chance? Just wondering.

Check out this link:
http://westlabs.com/Trannys.HTML#5watt

[kg6epv]

No, those are copies of our original designs. I don't know much about West Labs... But Matchless buys from us. Bob, TDS

[rocketeer]

Bob ..... thanks for recommendations on keeping supply current up and such. I will be doing some tests as to full power current pull on a MONO 6L6 and EL34 PP output section doing bursts right to clipping and some into clipping. Using a 100 watt amp PT that I already have should technically have twice what I need .... or we'll see. Then I will know what is necessary for the stereo version. Has anybody else performed tests like this? (somebody must have ...... come on.......)