Amp build ideas needed for massive transformer ...

4114Effects

Have a random transformer here - it's a beast of a thing, so I need suitably mad amp circuit suggestions to use it in.

Specs are:

5v at 3A
6.3v at 7A
75v at 100ma bias
450v at 250ma 

Ideas so far are some kind of valve bass amp - 2 or 4 KT88 should be no problem for the TX

Any more suggestions?

Ravenous

The 5V output makes me think of digital applications. So a valve amp with some madcap digital processors built into the front end..?

4114Effects

Ravenous said:

The 5V output makes me think of digital applications. So a valve amp with some madcap digital processors built into the front end..?

5v is for a valve rectifier

ICBM

250mA isn't a lot at 450V - that's barely enough for a typical 50W amp.

Ravenous

4114Effects said:

Ravenous said:

The 5V output makes me think of digital applications. So a valve amp with some madcap digital processors built into the front end..?

5v is for a valve rectifier

Heh I have never poked around in a valve amp, so I wondered why on earth it would need 5V and 6.3V!

Thanks.

4114Effects

ICBM said:

250mA isn't a lot at 450V - that's barely enough for a typical 50W amp.

What a strange transformer it is then ... hmmm

ICBM

It's the 7A 6.3V rating that's surprising - even a pair of EL34s don't draw anything like that, and that's probably the highest power valve draw it would need to handle give the HT rating - but what if it's designed for something with a huge number of preamp valves...

All-valve digital modelling amp?

Ravenous

ICBM said:

All-valve digital modelling amp?

About the size of a Google server building, and preferably built in Greenland to save on the cooling bills....

normula1

Perhaps it's from a hi-fi amp which would have double the number of valves.

ICBM

normula1 said:

Perhaps it's from a hi-fi amp which would have double the number of valves.

And in the old days, a - highly dangerous by modern standards! - multi-pin connector to supply a separate preamp with power, since they usually didn't have a PT of their own.

That would make sense. So you could be driving four EL34s in the power amp - although at fairly low audio output power, so no need for a big HT current - and possibly 6-10 preamp valves depending on how complex the preamp was.

Nomad

Four channel guitar amp, each channel having lots of gain options, and independent EQ, reverb and tremolo. Maybe some valves for silent switching?

MartinB

ICBM said:

It's the 7A 6.3V rating that's surprising - even a pair of EL34s don't draw anything like that, and that's probably the highest power valve draw it would need to handle give the HT rating - but what if it's designed for something with a huge number of preamp valves...

All-valve digital modelling amp?

From an old valve-based organ, perhaps?  Those had large numbers of preamp valves and usually only a small power amp, and are the kind of thing that might get broken up for parts nowadays. 

Modulus_Amps

is it a matchless spec PT, that heater current may have been used to power those little bulbs in the amp.... and some Christmas lights too

4114Effects

Modulus_Amps said:

is it a matchless spec PT, that heater current may have been used to power those little bulbs in the amp.... and some Christmas lights too

I could use it to power an amp and a load of LED stage lights ...

Which Matchless would use a B+ that high? Not the EL84 ones I'm guessing ...

Modulus_Amps

4114Effects said:

Modulus_Amps said:

is it a matchless spec PT, that heater current may have been used to power those little bulbs in the amp.... and some Christmas lights too

I could use it to power an amp and a load of LED stage lights ...

Which Matchless would use a B+ that high? Not the EL84 ones I'm guessing ...

No EL84's for sure, I would try something with big bottles, Like KT88's

4114Effects

Modulus_Amps said:

4114Effects said:

Modulus_Amps said:

is it a matchless spec PT, that heater current may have been used to power those little bulbs in the amp.... and some Christmas lights too

I could use it to power an amp and a load of LED stage lights ...

Which Matchless would use a B+ that high? Not the EL84 ones I'm guessing ...

No EL84's for sure, I would try something with big bottles, Like KT88's

Yeah, 2x KT88 into a 4.5k load seems about right for the TX. Maybe a Hifi amp ... hmmm

ICBM

Modulus_Amps said:

4114Effects said:

Which Matchless would use a B+ that high? Not the EL84 ones I'm guessing ...

No EL84's for sure, I would try something with big bottles, Like KT88's

The Phoenix is 2-EL34, although I don't know what the HT voltage is.

MartinB said:

From an old valve-based organ, perhaps?  Those had large numbers of preamp valves and usually only a small power amp, and are the kind of thing that might get broken up for parts nowadays.  

Good call. It must be something of this general spec, anyway.

4114Effects

ICBM said:

Modulus_Amps said:

4114Effects said:

Which Matchless would use a B+ that high? Not the EL84 ones I'm guessing ...

No EL84's for sure, I would try something with big bottles, Like KT88's

The Phoenix is 2-EL34, although I don't know what the HT voltage is.

MartinB said:

From an old valve-based organ, perhaps?  Those had large numbers of preamp valves and usually only a small power amp, and are the kind of thing that might get broken up for parts nowadays.  

Good call. It must be something of this general spec, anyway.

Deffo not from an organ. It's a modern production TX from Danbury. 

normula1

ICBM said:

normula1 said:

Perhaps it's from a hi-fi amp which would have double the number of valves.

And in the old days, a - highly dangerous by modern standards! - multi-pin connector to supply a separate preamp with power, since they usually didn't have a PT of their own.

That would make sense. So you could be driving four EL34s in the power amp - although at fairly low audio output power, so no need for a big HT current - and possibly 6-10 preamp valves depending on how complex the preamp was.

I inherited one of those. The mains lead came into the preamp chassis which had the power switch and from there was a two pin AC power cable to the power amp chassis and a separate eight pin Bulgin? plug for the pre-amp signal going one way and DC power and heater going the other way. This connector also provided ground.

I still have the power chassis albeit now fitted with a proper IEC mains socket and the eight way connector well and truly disconnected

ICBM

It wasn't uncommon to have the mains cable going to the power amp, but the on/off switch on the preamp - next to the controls obviously - so the multi-pin connector carried ground, signal (x2 if stereo), filaments, HT (usually around 250VDC) and two live mains wires, one unswitched... all down a lashed-up cable bundle with some shielded and some unshielded wires all in a loose rubber sleeve!

martinw

I know what it is!