Selectable B+

[MGW]

Anyone ever use a dual secondary with a switch to switch between the B+ voltages. I'm toying with the idea of using a frafo with 600v and 550v secondaries and I'm thinking it may be cool to be able to switch between the two depending on the mood I'm in.

And the important queston...how will this work on an express? and am I asking for trouble?

Thoughts?

[martin manning]

I'm pretty sure I've seen this come up before, and the result was the Express sounded best at Express voltages. Maybe someone else can recall the details and/or thread.

[darryl_h]

Wouldn't a VVR achieve the same result?

[ToneMerc]

Courtesy of George M

http://metroamp.com/wiki/index.php/Dual ... _switching

http://valvestorm.com/Products/Switches

TM

[Cantplay]

Take a look at the Ampmaker double six.

Www.ampmaker.com

It goes 1, 6, or 12 watts.

I have one under construction now.

John

[M Fowler]

Anyone ever use a dual secondary with a switch to switch between the B+ voltages. I'm toying with the idea of using a frafo with 600v and 550v secondaries and I'm thinking it may be cool to be able to switch between the two depending on the mood I'm in.

And the important queston...how will this work on an express? and am I asking for trouble?

Thoughts?

The switch is simple enough but on fixed bias like the Express you need to change the bias when you switch so the posted Metro switch info would be the best bet for your application. On my Martin Manning designed PCB Express I used a HT switch but so far I haven't added bias switching but I really should. The amp sounds best on higher HT but again that is without bias change so that makes a big difference.

Mark

[tubeswell]

I did a SE with switchable B+ (and rect tubes and output tubes) a couple of years ago.

[img1191]http://farm9.staticflickr.com/8029/8031 ... 9886_o.jpg[/img]

I have attached some notes on the different voltages I got:

[wyatt]

I did this for a short while on a 5E3 clone, swapping between the high voltages my original 1960 Deluxe produced on modern 120VAC wall voltage and the lower voltage of a compensated windings.

Was there a difference? Yes. Was there a significant difference? No. I don't think the difference was enough that if I walk away from the amp for a few days and came back I could tell which B+ it was set at. I think in similar situations someone would decide which one they prefer and keep the switch there 99% of the time. So, eventually, I removed the switch and hardwired in the lower compensated voltage.

[M Fowler]

In cathode bias amp like the Zwreck I installed the HT and use the function some times, usually I keep it on higher voltage.

I also did this dual HT switching on several Reverb Rocket builds a few years ago, but it also had 18w/36w switching.

[katopan]

I'm building my Express style amp with a PT with 300-275-225-0-225-275-300 HT secondary. But it's more for selecting voltages appropriate to different output valves rather than power reduction. As already mentioned you do have the problem of tracking the bias along with the B+, which Dana's VVR for fixed bias amps will do.

[Colossal]

I've tried it on a Liverpool variant and an Express and in both cases, I preferred the higher B+. There wasn't much of a volume reduction at the reduced seconday voltage, but the amps both lost the extra something...transparency, clarity, chime, presence. I added the B+ select switch just to answer the question of what do the different voltages sound like, but would not do it again. Both amps sounded best at their design voltages. FWIW, IMHO.

[MGW]

In cathode bias amp like the Zwreck I installed the HT and use the function some times, usually I keep it on higher voltage.

I also did this dual HT switching on several Reverb Rocket builds a few years ago, but it also had 18w/36w switching.

I'm actually building a Rocket and an Express and was thinking of using this on the Rocket. However, your 18W/36W swtich intrigues me. Is it something fairly simple to do? I'm building the amp for one my friends at church and half power would be quite useful.

[M Fowler]

In cathode bias amp like the Zwreck I installed the HT and use the function some times, usually I keep it on higher voltage.

I also did this dual HT switching on several Reverb Rocket builds a few years ago, but it also had 18w/36w switching.

I'm actually building a Rocket and an Express and was thinking of using this on the Rocket. However, your 18W/36W swtich intrigues me. Is it something fairly simple to do? I'm building the amp for one my friends at church and half power would be quite useful.

Very easy to do.

[sliberty]

I believe Ceriatone's Rock It has dual secondaries and a switch. Check their layout.

[MGW]

Nice. I see the B+ switching also. Good deal. So with either of these switches...does the amp need to be powered down or in standby to switch them?