amp project

Hennie · 08-20-2006, 08:36 PM

Im trying to build a tube amp with a transformer rated at 350v not c/tapped will it work? the o/transformer is 6600p/p rated at 35w. What tubes do I use 6L6's?

Mark Lavelle · 08-21-2006, 04:56 AM

Quote:

Originally Posted by Hennie

Im trying to build a tube amp with a transformer rated at 350v not c/tapped will it work? the o/transformer is 6600p/p rated at 35w. What tubes do I use 6L6's?

1. You'll get a bit under 500VDC with a full wave bridge (unless that 350VAC is just an unloaded measurement, in which case you'll get significantly lower DC out).

2. Everything else depends on how much current that power transformer can safely supply. Do you have specs? If it's pulled from old equipment one can also make an educated guess about the specs from a list of the tubes in that old box (assuming it was some kind of audio circuit).

Merlinb · 08-21-2006, 04:15 PM

With a silicon bridge rectifier you can expect an HT of about 410V under load.
You could also make a hybrid valve/silicon rectifier to drop the voltage down to 350V or so, depending on the valve used.

The output transformer is suitable for
6L6
6L6GC,
6V6,
EL84(but only at a lower HT of 300V or less)

Hennie · 08-23-2006, 07:48 PM

Hi there guys, Sorry about the delay but I am not pemanently connected on the net as I am staying in South Africa.(Costs)Thanx for the feedback on my question.Hope you can help me again on this one.The raa for 2 EL34 tubes is 3K4ohms.Does it change when I want to use 4 tubes?Any links where I can read up on this
Thanx Hennie.

DirtyGeorge · 08-29-2006, 06:12 PM

The load impedance halves when the tubes double. A 100W Marshall OT is 1750 ohms.

DG

Hennie · 09-03-2006, 07:54 PM

Thanks for the answer.I thought it would be more or less the same.I had a 100w output transformer wound at 3k4 Raa. What output tubes can I safely use .Even if I get 80w output I would be happy.Any help on this one?

Ray Ivers · 09-03-2006, 08:12 PM

Hennie,

A 100W, 3,400 ohm OT? I can't recall having seen one of these before, but IMO it would work just fine for two good KT90's , KT88's, or EL34's at that B+ (my simulator program indicates about 450V) which should give you maybe 60W or so in AB1. Four 6L6-type tubes will also work with this loading, and should provide about 90-100W (proving the PT is up to the task). These are by no means the only tube options available, only my top personal picks for this B+ and OT.

Bear in mind that the output-power thing is just a best-guess until the meter tells it's tale.

Ray

Hennie · 09-04-2006, 06:10 PM

Thanks Ray, I think I'll go for the 6L6 option.The transformer coil is 60mm thick and 95mm high. It was wound by an old guy who's done it for 40 years.I think the Tranny will do the job.Ive ordered myself a power transformer 350-0-350 at 450ma with a 60v bias tapping. The heater windings is 3.15-0-3.15 rated at 6a and another one rated at 3a.I think it would do the job.Funny thing is he said I only need a 8H choke. Any help on this?

08-20-2006, 08:36 PM	#1
Hennie Junior Member Join Date: Aug 2006 Posts: 8	amp project Im trying to build a tube amp with a transformer rated at 350v not c/tapped will it work? the o/transformer is 6600p/p rated at 35w. What tubes do I use 6L6's?

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08-21-2006, 04:15 PM	#3
Merlinb Senior Member Join Date: Aug 2006 Location: Yorkshire Posts: 192	With a silicon bridge rectifier you can expect an HT of about 410V under load. You could also make a hybrid valve/silicon rectifier to drop the voltage down to 350V or so, depending on the valve used. The output transformer is suitable for 6L6 6L6GC, 6V6, EL84(but only at a lower HT of 300V or less)

08-23-2006, 07:48 PM	#4
Hennie Junior Member Join Date: Aug 2006 Posts: 8	Hi there guys, Sorry about the delay but I am not pemanently connected on the net as I am staying in South Africa.(Costs)Thanx for the feedback on my question.Hope you can help me again on this one.The raa for 2 EL34 tubes is 3K4ohms.Does it change when I want to use 4 tubes?Any links where I can read up on this Thanx Hennie.

08-29-2006, 06:12 PM	#5
DirtyGeorge Member Join Date: Jun 2006 Location: Germantown, MD Posts: 59	The load impedance halves when the tubes double. A 100W Marshall OT is 1750 ohms. DG

09-03-2006, 07:54 PM	#6
Hennie Junior Member Join Date: Aug 2006 Posts: 8	Thanks for the answer.I thought it would be more or less the same.I had a 100w output transformer wound at 3k4 Raa. What output tubes can I safely use .Even if I get 80w output I would be happy.Any help on this one?

09-03-2006, 08:12 PM	#7
Ray Ivers Lifetime Member Join Date: Jun 2006 Location: Connecticut Posts: 442	Hennie, A 100W, 3,400 ohm OT? I can't recall having seen one of these before, but IMO it would work just fine for two good KT90's , KT88's, or EL34's at that B+ (my simulator program indicates about 450V) which should give you maybe 60W or so in AB1. Four 6L6-type tubes will also work with this loading, and should provide about 90-100W (proving the PT is up to the task). These are by no means the only tube options available, only my top personal picks for this B+ and OT. Bear in mind that the output-power thing is just a best-guess until the meter tells it's tale. Ray

09-04-2006, 06:10 PM	#8
Hennie Junior Member Join Date: Aug 2006 Posts: 8	Thanks Ray, I think I'll go for the 6L6 option.The transformer coil is 60mm thick and 95mm high. It was wound by an old guy who's done it for 40 years.I think the Tranny will do the job.Ive ordered myself a power transformer 350-0-350 at 450ma with a 60v bias tapping. The heater windings is 3.15-0-3.15 rated at 6a and another one rated at 3a.I think it would do the job.Funny thing is he said I only need a 8H choke. Any help on this?

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