Hammond 273BX PT question

[navdave]

I got one of these for a Sunn Solarus I'm fixing that had a burnt transformer. Just curious if it matters which primary tap I use 115v or 125v? My wall socket varies between 120v-123v.
http://www.tubesandmore.com/sites/default/files/associated_files/p-t273bx.pdf

[kagliostro]

I think you can implement a Spongy / Bold switch a la Mesa Boogie 




K

[navdave]

Hmmm good read I think I may use the 125v tap as for a bold/spongy switch I don't really want to go drilling new holes into a 42 year old amp cheers fellas 🍻

I would use the 125 volt tap.   

If you want to use the 115 v tap, then I would consider building a buckerdown transformer as shown in Sluckey's scrapbook.   This a link to a discussion, on why you may decide not to use the 115v tap.   http://www.geofex.com/article_folders/vintvolt/vintvolt.htm

[kagliostro]

It was a joke, with a difference of a few volts I think the difference in tone will be very, very small


as to reproduce a spongy/bold effect it will be interesting to know the real spongy/bold gap of voltage on secondaries of the Mesa as to know which is the difference in volt planned on the primary winding


Ciao


K

[kagliostro]

Usually tollerance in voltage supply for the heater is in the order of  ±20%

However I don't know how much vary the voltage on the heater and on B+ switching between sponge and bold

K

[PRR]

> voltages on filaments

There's no change in heater voltages.

Wrong.

[kagliostro]

Hi PRR

There's no change in heater voltages.

Excuse me, but I doubt that there isn't a change in heater voltage, considering that the sponge/bold switch acts on the primary winding of the PT

Please, if I misunderstand what you were saying, or the whole thing, can you explain it me better ?

Thanks

Franco


p.s.: I was refering to the heater voltage change as a parameter to be used as to establish the difference in voltage between the primary intakes used for sponge and bold

[navdave]

The Sentura and Solarus are the same animal. With some revisions to the solid state power supply and preamp filtering in newer models.

http://el34world.com/charts/Schematics/files/sunn/Sunn_SENTURA_I_and_SOLARIS.pdf

[ernie_jr]

This P/T is a little under voltage for SUNN amps. Sunn amps ran 400-400 or 410-410 depending on year. This P/T is 350-350.
M2C
Ernie

[navdave]

Yeah but the voltages are right maybe 25-30 volts under the ones on the old schematics.

This P/T is a little under voltage for SUNN amps. Sunn amps ran 400-400 or 410-410 depending on year. This P/T is 350-350.
M2C
Ernie

[navdave]

Well if I used the 115 tap the all the b+ voltages after rectification are right at spec but the heater supply for the heater supply are pretty high like 5.7 for the rec tube and 7.2 for the tubes.

After reading the posts, and the initial post,

My question is:  Is this your amp or is it an amp for a customer.  Under the assumption that it is not yours.  Then ernie_jr raises a good point.  The p/t should be closer to what Sunn originally provided.  Unless the customer is aware the tone of the amp is likely to change with the proposed P/T replacement, the proposed transformer should not be used.

Going back to voltage selection, Get you self a vintage amp saver, and wire temporarily wire the amp at 115v, (The amp was designed for an input voltage of 117V), then allow the customer to play the amp at the various voltages.  If the tone at this point is not important, then permanently wire the transformer at 125v. (You will probably have to tweek the output bias).  If tone is important, then you might also have a sale for a vintage amp saver. 

A couple of things you have done.
1.   You made sure your customer had input.  This builds trust, leads and loyalty.
2.   You just had a teaching moment with the customer,  You taught the customer how important line voltage is to the vintage amp operation. 

Good luck

Thanks navdave for the info, I missed the labeling.

[navdave]

@drgonzonm Customer bought the amp dead he's never heard it before he's buys a lot like this. He's defiantly not a cork sniffer he just likes to play loud as hell with fuzz and Sunn's deliver well in the loud department. Cheers and thanks for all the input!

[ernie_jr]

if you use a solid state rectifier, it will put you closer to the  sunn  voltages without changing the filament voltages.
ernie