Hi,

Can I use a Hammond 300BX power trans for the Mullard 5-20 circuit? So
that I regulate with tube rectifier (5U4) ? Please advise...

Thanks !

Hi,

Can I use a Hammond 300BX power trans for the Mullard 5-20 circuit? So
that I regulate with tube rectifier (5U4) ? Please advise...


Sure, it has plenty of current to handle the 5-20 circuit, even a pair.

On my 5-20 hom brew project this is what I experienced when creating them
with Hammond (and one Leslie Choke) iron.....

I used a 278X on my 5-20 Mono-Block clones as I went by the spec in the
Mullard Book, i.e. the closest technical match.

The only problem with this choice is that the 6.3 VAC was killing the
filaments of the EL34's. I had to place a parallel load resistor to get the
EL34 filaments down to 6.35 Volts from 7.4 Volts. Plus, running the 6.3 Volt
section at half load made the rest of the secondary DC voltages about 20%
higher than required. Now that I modded the section it works well. In
reality the whole 6.3 Volt section should ideally be rated at 1.5A el34 +
1.5 A el34+ .3 A 12ax7 + .2A ef86= 3.5 amps or more like 4 amps is a desired
value. The Hammonds provide 6 amps, a bit or overkill for a 5-20 Monoblock
design.

The power tubes used to make noises when warming-up, but after a power
resistor mod the tubes are now calmed down and the filaments don't shine
like light bulbs any more.

One other thing to note is that the original Mullard schematic calls for a
very special Choke; 10H that measures 200 Ohms DC resistance. Here you will
also need to compensate or even do away with the choke and use a 200 Ohm 10
watt resistor instead (the choke PSU will probably sound better.)

Another note is that you can probably get away with implementing a Power
Transformer that has less than the specified 410-0-410 from the Mullard
Book.

I would venture to say that a Hammond 274 BX or 374 BX are a closer match
for a Monoblock 5-20 amp and one can then use a modern Choke with a DCR of
around 90 to125 Ohms (Hammond Models 193G, 159Q or 158Q) which are readily
available and should handle the DC current required by the 5-20.

For one I could never find a 10H Choke with 200 ma rating that measured 200
Ohms DC. You may not have to pay attention to the DC filament voltage as
with the 278X. A modern Hammond choke with a 150 ma rating should suffice,
giving a bit less resulting inductance but is OK electrically. I used the
Leslie Chokes from the original Leslie 147 amp chassis. You can also use the
193J Choke which would be the ideal choice, but you will need to play with
the PSU Pi Filter series resistance to tweak the final DC voltages in.

I had to resort to implementing two mods: One, installing some 120 Ohm 10
watt Voltage Control resistors on each of the Tube Rectifier's plates and
also created the 200 Ohm DC resistance by using an original Hammond 147
amplifiers Choke (58 to 60 Ohm DCR) with a 150 Ohm 10 watt resistor for
approx 210 Ohm DCR in the PSU. This tweaked the final DC voltages properly.
I probably could have saved all this grief if I had known about using a
370-0-370, 200 milliamp Transformer instead.... oh well live and learn.

My experience with Hammond Power Transformers is that they are
conservatively rated and can deliver the full rated current without a
problem. It's the final regulation of the amplifier's voltages which is the
key to biasing the 5-20 amp properly. As with any home brew project its
always best to power up the amp with a variable DC power supply and check
the current draw so from there one can choose the best drop-in Power
Transformer to use.

If I recall correctly, the 5-20 amp uses a 470 Ohm, 3 watt (use a 5 watt,
better choice) power resistor in the Cathode of each power tube bypassed by
a 50 uf Electrolytic cap. The voltage drop across this resistor should be
about 32 Volts DC for 68 milliamps current, yup they run the EL34's kinda
hot! This amp can go through slimmy EL34's like crazy. I would only use
Svetlana or Sovtek 6CA7 Fat Bottle tubes. JJ are the next choice. I have
tried the Ei nipple tops and the Sovtek EL34WXT and the plated go cherry-red
after 3 min.

The 5Volt Hammond sections have mornally 3 amps in both cases so a 5U4 will
work well in case you need to tame the final DC quiescent voltages a bit. I
have used succesfully GZ37 and 5U4G in mine. I have not been able to use
GZ34 as the filament voltage is still a bit too high and the tube filament
looks like it's going to burn out. Heck, I just may change the Power
Transformers in the near future to the 274 BX and save the 278X for a KT88
project.

But you may need the 220V primary which will require that you implement the
374BX or 274 BX..... the 302 AX is the biggest recommende choice. I would
not use a 300 BXm, it is way over dimensioned for a 5-20, in fact one RAT
fellow recommended that for a Stereo Single Chassis Version, but it would
need to have at least 320 ma in the secondary and 8 amps in in the 6.3 Volt
Section plus at least 4 amps in the 5 volt section to run dual GZ34's (for
longevity sakes).

My 5-20's are undergoing some parts upgrades (Auricaps) and a rework of the
internal wiring, you can see them at http://www.shermanaudio.com

Hope these tips help you out!!!

Regards,

Rich Sherman

Rich Sherman wrote:

On my 5-20 hom brew project this is what I experienced when creating them
with Hammond (and one Leslie Choke) iron.....

I used a 278X on my 5-20 Mono-Block clones as I went by the spec in the
Mullard Book, i.e. the closest technical match.

The only problem with this choice is that the 6.3 VAC was killing the
filaments of the EL34's. I had to place a parallel load resistor to get the
EL34 filaments down to 6.35 Volts from 7.4 Volts. Plus, running the 6.3 Volt
section at half load made the rest of the secondary DC voltages about 20%
higher than required. Now that I modded the section it works well. In
reality the whole 6.3 Volt section should ideally be rated at 1.5A el34 +
1.5 A el34+ .3 A 12ax7 + .2A ef86= 3.5 amps or more like 4 amps is a desired
value. The Hammonds provide 6 amps, a bit or overkill for a 5-20 Monoblock
design.

Rich, did you check your supply voltage? All your measurements lead me
to suspect the line may have been on the high end. Watching quite a few
of the posts over at the antique radio forum over the past few years
indicates high line voltage to be a common problem. Hammond is
not normally that as far of the mark as you have indicated for the
heater voltage.

A simple fix that would probably set all your voltages into the correct
ball park would be a resister on the primary side of the 278X. A more
sophisticated remedy would use a common 6 or 12 volt heater transformer
in series bucking with the supply. That would result in better regulation of
the resulting voltages than any of the resistor fixes.

Extra loading such as your resistor across the heater supply is not a good fix.
It results in more transformer heating as well as the extra watts probably
dissipated under the chassis by the load resistor.

Good Luck, John Stewart

Hi John:

I am currently re-building the amps at home with some upgraded components
and also doing away with some terminal/spade strips and now soldering all
the connections for more secure electrical connections.

The power cords are also going to be changed for new ones; probably 12 Gauge
at least.

Using the Hammond 278X Power Transformer has always provided far more
voltage that was required for my 5-20 project, despite my mains being at
117 -120 VAC most of the time, rarely going over 120 VAC.

But, I now own a nice Variac which I did not have before. Testing with
several line voltages should give me a better clue as to exactly what I need
to adjust for the optimum DC PSU voltage distribution.

Your tips are excellent, and I have to agree that loading down the filament
section with power resistors was not the best route, although it did allow
my EL-34's to run a 6.4 VAC vs the more than 7 VAC I used to get and settled
the amps down, despite the under chassis heat.

I do find though that not all EL34's can handle 68 milliamps for extended
periods. Seems that in the 50's and 60's the tendency of designers was to
run the EL34's hot, what do you think, was this a common trend? Isn't 68 ma
a bit too much for an EL34 tube? I would think that a EL34 Push-pull amp
should not exceed 60 ma at most for tube longevity sakes, or at least be 20%
under maximum plate dissipation.

This weekend I hope to complete the upgrades and testing. I will report back
on what I find the following week.

Thanks for your attention and good advice.

BR/
Rich

Thinking about what I has written I perused the Mullard book last night
while sipping some hot tea as I have had a bad cold for the last 8 days!

My 6 week trip to Sweden made me end up with Bronchitis as it got pretty
cold there after a November snowfall.

Comparing the Mullard book specs to the Hammond that I used:

Mullard spec Hammond 278X
410-0-410 Volts AC @ 180 ma. 400-0-400 @ 200 ma
3.15-0-3.15 Volts AC @ 4.5 A 3.15-0-3.15 Volts AC @ 6A
5 - 0 Volts AC @ 3A 5 - 0 Volts AC @ 3A

It is for this reason that the model I chose cannot simply drop into the
5-10 schematic and work, unless I compensate
for the extra current capacity to regulate the final voltages to their
proper levels.

The Triode Electronics site has very nice Dynaco replacement iron that is
designed to 'drop into' existing Dynaco amps
with no mods. This is only possible if the Power Transformer is a duplicate
of the original. If one tries to match a Hammond
transformer to what the specs are in the Triode Site, it becomes evident
that modifications will be necessary to adapt
the Hammond iron to any pre-existing design.

In my humble opinion the best thing for building a 5-10 amp would be to
order an 'exact' Mains Transformer and Choke combination
from Sowter. I believe thay have the Output Transformer already built for
that purpose and the Mains + Choke are available at no extra
cost.

With Hammond I know that their cost to custom wind iron becomes extremelly
reasonable only when one one orders 5 pieces or more.
And the price to wind 10 or 20 custom pieces (of the same) is dirt cheap,
about 10 to 20 USD a piece for a hefty mains tranformer.
It seems that once the production line is going, winding by the dozen saves
a person alot of money.

Sowter seems the better 'one wind' company. Bartolucci makes very attractive
Iron and is in the business to wind custom transformers.

One interesting thing that I notice about the Hammond Power Transformer
product line is that they all appear to be
designed mostly for Mono-Block centric amplifiers. It is very difficult to
find a current production Hammond Power Transformer
to build a good 6L6, EL34 or 6550 Stereo Amp. I wrote to Mark Mercer at
Hammond about this, but never received a response.

in article , Rich Sherman at
wrote on 12/2/04 9:58 AM:

Thinking about what I has written I perused the Mullard book last night
while sipping some hot tea as I have had a bad cold for the last 8 days!

My 6 week trip to Sweden made me end up with Bronchitis as it got pretty
cold there after a November snowfall.

Comparing the Mullard book specs to the Hammond that I used:

Mullard spec Hammond 278X
410-0-410 Volts AC @ 180 ma. 400-0-400 @ 200 ma
3.15-0-3.15 Volts AC @ 4.5 A 3.15-0-3.15 Volts AC @ 6A
5 - 0 Volts AC @ 3A 5 - 0 Volts AC @ 3A

It is for this reason that the model I chose cannot simply drop into the
5-10 schematic and work, unless I compensate
for the extra current capacity to regulate the final voltages to their
proper levels.

*** I might have missed something in the thread, but it looks to me that
the Hammond is a PERFECT replacement. Older transformers typically used
117V or so as the mains input. Modern utilities deliver 120-125 VAC, at
least in my neighborhood.

*** I often find with old gear that I have to take steps to reduce the B+
voltage because of the higher mains voltages. If you measure 120 VAC from
your outlet, you'll be right on the money.


One interesting thing that I notice about the Hammond Power Transformer
product line is that they all appear to be
designed mostly for Mono-Block centric amplifiers. It is very difficult to
find a current production Hammond Power Transformer
to build a good 6L6, EL34 or 6550 Stereo Amp.

*** That may be so, but there are a lot of old tube organs that don't work
very well (ya know, the ones over 40 ;-) and often the trannies in them are
cheap and powerful. I've got a PS transformer from a CONN organ that ought
to do the trick.

Jon

Well, I intend to build both channel in 1 chasis (integrated). Would
it be more than enough if I used Hammond 300BX?

Please have a look to the below schematic, its a Dynaco Modified
Mullard Circuit :-

http://www.triodeel.com/dynamull.gif

Instead of 8H choke, I changed it to 10H (200mA). The rest almost the
same. I am using the Hammond 1650P OPT. Any comments?

Kind regards!


"Rich Sherman" wrote in message . ..
On my 5-20 hom brew project this is what I experienced when creating them
with Hammond (and one Leslie Choke) iron.....

I used a 278X on my 5-20 Mono-Block clones as I went by the spec in the
Mullard Book, i.e. the closest technical match.

The only problem with this choice is that the 6.3 VAC was killing the
filaments of the EL34's. I had to place a parallel load resistor to get the
EL34 filaments down to 6.35 Volts from 7.4 Volts. Plus, running the 6.3 Volt
section at half load made the rest of the secondary DC voltages about 20%
higher than required. Now that I modded the section it works well. In
reality the whole 6.3 Volt section should ideally be rated at 1.5A el34 +
1.5 A el34+ .3 A 12ax7 + .2A ef86= 3.5 amps or more like 4 amps is a desired
value. The Hammonds provide 6 amps, a bit or overkill for a 5-20 Monoblock
design.

The power tubes used to make noises when warming-up, but after a power
resistor mod the tubes are now calmed down and the filaments don't shine
like light bulbs any more.

One other thing to note is that the original Mullard schematic calls for a
very special Choke; 10H that measures 200 Ohms DC resistance. Here you will
also need to compensate or even do away with the choke and use a 200 Ohm 10
watt resistor instead (the choke PSU will probably sound better.)

Another note is that you can probably get away with implementing a Power
Transformer that has less than the specified 410-0-410 from the Mullard
Book.

I would venture to say that a Hammond 274 BX or 374 BX are a closer match
for a Monoblock 5-20 amp and one can then use a modern Choke with a DCR of
around 90 to125 Ohms (Hammond Models 193G, 159Q or 158Q) which are readily
available and should handle the DC current required by the 5-20.

For one I could never find a 10H Choke with 200 ma rating that measured 200
Ohms DC. You may not have to pay attention to the DC filament voltage as
with the 278X. A modern Hammond choke with a 150 ma rating should suffice,
giving a bit less resulting inductance but is OK electrically. I used the
Leslie Chokes from the original Leslie 147 amp chassis. You can also use the
193J Choke which would be the ideal choice, but you will need to play with
the PSU Pi Filter series resistance to tweak the final DC voltages in.

I had to resort to implementing two mods: One, installing some 120 Ohm 10
watt Voltage Control resistors on each of the Tube Rectifier's plates and
also created the 200 Ohm DC resistance by using an original Hammond 147
amplifiers Choke (58 to 60 Ohm DCR) with a 150 Ohm 10 watt resistor for
approx 210 Ohm DCR in the PSU. This tweaked the final DC voltages properly.
I probably could have saved all this grief if I had known about using a
370-0-370, 200 milliamp Transformer instead.... oh well live and learn.

My experience with Hammond Power Transformers is that they are
conservatively rated and can deliver the full rated current without a
problem. It's the final regulation of the amplifier's voltages which is the
key to biasing the 5-20 amp properly. As with any home brew project its
always best to power up the amp with a variable DC power supply and check
the current draw so from there one can choose the best drop-in Power
Transformer to use.

If I recall correctly, the 5-20 amp uses a 470 Ohm, 3 watt (use a 5 watt,
better choice) power resistor in the Cathode of each power tube bypassed by
a 50 uf Electrolytic cap. The voltage drop across this resistor should be
about 32 Volts DC for 68 milliamps current, yup they run the EL34's kinda
hot! This amp can go through slimmy EL34's like crazy. I would only use
Svetlana or Sovtek 6CA7 Fat Bottle tubes. JJ are the next choice. I have
tried the Ei nipple tops and the Sovtek EL34WXT and the plated go cherry-red
after 3 min.

The 5Volt Hammond sections have mornally 3 amps in both cases so a 5U4 will
work well in case you need to tame the final DC quiescent voltages a bit. I
have used succesfully GZ37 and 5U4G in mine. I have not been able to use
GZ34 as the filament voltage is still a bit too high and the tube filament
looks like it's going to burn out. Heck, I just may change the Power
Transformers in the near future to the 274 BX and save the 278X for a KT88
project.

But you may need the 220V primary which will require that you implement the
374BX or 274 BX..... the 302 AX is the biggest recommende choice. I would
not use a 300 BXm, it is way over dimensioned for a 5-20, in fact one RAT
fellow recommended that for a Stereo Single Chassis Version, but it would
need to have at least 320 ma in the secondary and 8 amps in in the 6.3 Volt
Section plus at least 4 amps in the 5 volt section to run dual GZ34's (for
longevity sakes).

My 5-20's are undergoing some parts upgrades (Auricaps) and a rework of the
internal wiring, you can see them at http://www.shermanaudio.com

Hope these tips help you out!!!

Regards,

Rich Sherman

in article , ADAM at
wrote on 12/5/04 10:54 AM:

Well, I intend to build both channel in 1 chasis (integrated). Would
it be more than enough if I used Hammond 300BX?

Please have a look to the below schematic, its a Dynaco Modified
Mullard Circuit :-

http://www.triodeel.com/dynamull.gif

Instead of 8H choke, I changed it to 10H (200mA). The rest almost the
same. I am using the Hammond 1650P OPT. Any comments?

Kind regards!



Adam,

I appreciate your post for another reason: I recently picked up a pair of
Dynaco A420 transformers and was looking for a circuit to use with them.

If you're looking for a better and more versatile chassis than what Hammond
offers, look at www.yaegeraudio.com. I also have a 3" high chassis that I
haven't put on the site yet (so far behind)

Good luck

Jon

Hi all:

Yesterday I spent the afternoon putting my Mullard 5-20 amps back together
again, after Humpty-Dumpty took them apart.

As suggested by John, and truly so, the mains voltage at my home is about
123VAC-125 VAC. Connecting this to the re-done 5-20 amps caused the voltages
on my amps to be much higher than ideal as always was the case.

Across the Cathode Resistor I read 37.3 volts DC (not the 32 Volts that the
Mullard Book shows). In addition, instead of the 465 Volts on the GZ34
rectifier to the first PSU cap I was reading close to 492 Volts DC! Ouch!

As the amps were 100% restored to all original schematic values; out came my
new Variac and I connected them up again, this time with the ability to
'throttle' the mains voltage.

To my surprise, when I adjusted the Variac to 115 VAC the Cathode Resistior
DC drop was exactly 31.8 VDC (ust about the required 32 VDC!).

DC voltage on the first cap was at 465 VDC by the book. The rest of the DC
voltages matched the manual exactly of +/- 3%.

As I had assumed, the Hammond iron that I used was just a bit over
dimensioned for the application. My next step will be to custom order a set
of Mains Iron to match the original Mullard specification and save me from
having to always Variac these amps.

I guess custom Iron from Sowter, Hammond or even Bartolucci would be good.
But it's a 2005 project for now. My Variac will save these amps and allow me
to enjoy thesem until the final mains iron replacement.

Gosh... the 5-20 design sounds very nice.

My advice on making a home brew Mullard 5-20, stick to the manual as closely
as you can. It will save many hours of tweaking and a quad of two of EL34's!

Bye,

Rich

"Rich Sherman" wrote in message
...
Hi all:

Yesterday I spent the afternoon putting my Mullard 5-20 amps back
together
again, after Humpty-Dumpty took them apart.

(snip)

I would suggest a filament transformer to buck the primary what you
have now.

(snip)

Gosh... the 5-20 design sounds very nice.

That's certainly the consensus from the 1950's. I could not afford to
build one back then so settled for two 5-10's (but, unfortunately, not
with Partridge OPT's - too much bread for a student in the UK!) I ran
them both off one home brew P/S - can't remember the details but IIRC
it was a 350-0-350 (from a large pre-WW2 radio) with choke input. The
5-10's were also very nice - gave them away in 1970... pity... (but to
a friend, so OK!)

(snip)

Cheers,
Roger

Wouldn't leaving the 6.3V heater winding alone and using a separate
heater supply be a better idea all around? I had a lot of success in
the five-dollar-Dynaco days with using the 5V rectifier winding in
series with the primary to drop the other voltages and simply using a
separate heater supply. I used a transformer (for AC filaments) but a
regulated DC supply would be a lot better. Of course I never used tube
rectifiers, preferring the sound of solid state diodes when the filter
caps were bypassed properly.

"Rich Sherman" wrote in message
...
Hi all:

Yesterday I spent the afternoon putting my Mullard 5-20 amps back
together
again, after Humpty-Dumpty took them apart.

As suggested by John, and truly so, the mains voltage at my home is
about
123VAC-125 VAC. Connecting this to the re-done 5-20 amps caused the
voltages
on my amps to be much higher than ideal as always was the case.

(snip)

As I had assumed, the Hammond iron that I used was just a bit over
dimensioned for the application. My next step will be to custom
order a set
of Mains Iron to match the original Mullard specification and save
me from
having to always Variac these amps.

(snip)

I would suggest a filament transformer (6.3 VAC or 12.6 VAC, pick one)
to buck the primary of what you have now - can be quite a small one,
the secondary current rating could be less than 3 amps.

(snip)


Rich