Edit: Yes it is a Magnavox, found this:
https://audiokarma.org/forums/index.php?threads/magnavox-169aa-help.1007098/
and:
https://www.radiomuseum.org/r/magnavox_ch_amp_169aa.html
Found this 6V6 PP amp at the recycling center. Lots of parts for a Fender Princeton.
Power, output transformers etc.
https://audiokarma.org/forums/index.php?threads/magnavox-169aa-help.1007098/
and:
https://www.radiomuseum.org/r/magnavox_ch_amp_169aa.html
Found this 6V6 PP amp at the recycling center. Lots of parts for a Fender Princeton.
Power, output transformers etc.
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Put on a new 3 prong line cord, and tacked in some diodes for the rectifier.
I didn't expect much B+ but got 421 Volts - nice and high!
Put in a pair of 5881 s that were handy, to draw some current and I know too much heater current.
Got 30V on the 270R cathode resistor which is 111mA, B+ is 393 at this current - also nice!
This might make a nice Tweed Deluxe build with 6v6 s.
I didn't expect much B+ but got 421 Volts - nice and high!
Put in a pair of 5881 s that were handy, to draw some current and I know too much heater current.
Got 30V on the 270R cathode resistor which is 111mA, B+ is 393 at this current - also nice!
This might make a nice Tweed Deluxe build with 6v6 s.
Just looked at the 5E3 Deluxe that's so popular and it only has 3 controls so a nice fit for this
small chassis. Should be very easy to do. I'll probably do the Dumble Tweedle Dee version.
I started stripping it of the guts and noticed that the 100R resistors for the heater center tap
are tied to the power tube cathodes which are cathode biased around 30V. An easy way to
elevate the heaters good also for the PI that has a high cathode voltage. Interesting.
small chassis. Should be very easy to do. I'll probably do the Dumble Tweedle Dee version.
I started stripping it of the guts and noticed that the 100R resistors for the heater center tap
are tied to the power tube cathodes which are cathode biased around 30V. An easy way to
elevate the heaters good also for the PI that has a high cathode voltage. Interesting.
Wow, thank you! You are reading my mind.
I measured the transformer two days ago and have been meaning to post it here.
Applied 121.9 V plate to plate and got 2.46 V out.
Turns ratio = 121.9/2.46 = 49.55
Impedance ratio = 49.55^2 = 2455.2
4 ohm load Zin = 9820.8
I was just thinking today that it was probably designed for 3.2 ohms:
3.2 ohm load Zin = 7857 ohms, that sounds about right.
We plan to run a single speaker so it will have to be replaced. I do have a Fender Blues Jr OT that is exactly the same physical size.
I've ordered a cheap Tweed Deluxe OT clone.
I measured the transformer two days ago and have been meaning to post it here.
Applied 121.9 V plate to plate and got 2.46 V out.
Turns ratio = 121.9/2.46 = 49.55
Impedance ratio = 49.55^2 = 2455.2
4 ohm load Zin = 9820.8
I was just thinking today that it was probably designed for 3.2 ohms:
3.2 ohm load Zin = 7857 ohms, that sounds about right.
We plan to run a single speaker so it will have to be replaced. I do have a Fender Blues Jr OT that is exactly the same physical size.
I've ordered a cheap Tweed Deluxe OT clone.
I'll point out that both the original Magnavox and the Blues Jr output transformers are rather small, tiny
as compared to HiFi transformers. But guitar amps don't have to reach down to 20 Hz.
The Tweed Deluxe OT is about twice the weight.
Measured the Blues Jr transformer the same way:
Applied 121.7 V plate to plate and got 4.46 out.
Turns ratio = 121.7/4.46 = 27.3
Impedance ratio = 27.2^2 = 744.7
8 ohm load Zin = 5957 ohms or about 6K this transformer is used with EL84 tubes and I'm not sure if 6K is close to optimal for 6V6 s.
6V6GT data sheet provides 8K, 10K, and 12K plate to plate impedance examples with max power produced with 8Kpp.
I believe that this is a very cheap transformer using thin wire to save copper, primary DCR = 424 ohms
in contrast the Magnavox OT has a 275 ohm primary DCR.
Blues JR secondary DCR is .7 ohms, Magnavox is .1 ohm - much better.
If the output tubes idle at 70 mA total then the power in the transformer primary is:
(.035^2 x 212) x 2 = .52W pretty insignificant and even less for the Magnavox.
Now I'm very curious to measure the cheap Tweed Deluxe OT when it arrives.
Good that there's plenty of room on this chassis for a larger OT.
as compared to HiFi transformers. But guitar amps don't have to reach down to 20 Hz.
The Tweed Deluxe OT is about twice the weight.
Measured the Blues Jr transformer the same way:
Applied 121.7 V plate to plate and got 4.46 out.
Turns ratio = 121.7/4.46 = 27.3
Impedance ratio = 27.2^2 = 744.7
8 ohm load Zin = 5957 ohms or about 6K this transformer is used with EL84 tubes and I'm not sure if 6K is close to optimal for 6V6 s.
6V6GT data sheet provides 8K, 10K, and 12K plate to plate impedance examples with max power produced with 8Kpp.
I believe that this is a very cheap transformer using thin wire to save copper, primary DCR = 424 ohms
in contrast the Magnavox OT has a 275 ohm primary DCR.
Blues JR secondary DCR is .7 ohms, Magnavox is .1 ohm - much better.
If the output tubes idle at 70 mA total then the power in the transformer primary is:
(.035^2 x 212) x 2 = .52W pretty insignificant and even less for the Magnavox.
Now I'm very curious to measure the cheap Tweed Deluxe OT when it arrives.
Good that there's plenty of room on this chassis for a larger OT.
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It might be worth popping in some tubes and trying the Magnavox OT with an 8-ohm load. It'd be a 17K plate-to-plate load, so you'd have to adjust the R113 cathode bias appropriately to work with the flatter load-line, but it might sound just fine despite the impedance mismatch. 6V6s are pretty forgiving tubes. On the other hand, a replacement OT specific to your design is easy to come by.
I bought the cheap version of the #041318 which I've seen listed as a Fender number and also a Heyboer.
Here it is in the more expensive ($57) Heyboer version at Tubeaudiosupply:
https://www.tubeaudiosupply.com/pro...ut-transformer-heyboer-usa-made-041318-125a1a
Note that it is listed for both the Tweed Deluxe and the Blackface but if you read the fine print it says
that the 5E3 Tweed used an 8K primary OT and this one is 6.6K. It is actually the Deluxe Reverb OT but
they say that it will work in the 5E3.
The one that I bought is also marked 041318 and 6.6K to 8 ohms but it was only $36 and it says made in Taiwan:
https://www.tubeaudiosupply.com/col...put-transformer-replacement-for-041318-125a1a
It arrived, and weighs 1.54 lbs which is middle of the road for a 20W OT.
Applied 122.5V in and got 4.37V out on the 8 ohm tap.
Turns ratio = 122.5/4.37 = 28.03
Imp ratio = 28.03^2 = 785.8
With an 8 ohm load = 6286 ohms
Primary DCR = 205.2 ohms
Secondary DCR = .8 ohms
These are much better than the Blues Jr OT
For the record the Blues Jr (actual Fender part) measures 14.9 oz = .93 lbs
And the Magnavox = 15 oz = .94 lbs
Note that this cheap Deluxe OT is about 1.5 times as heavy and might make a nice cheap Blues Jr OT upgrade.
Here it is in the more expensive ($57) Heyboer version at Tubeaudiosupply:
https://www.tubeaudiosupply.com/pro...ut-transformer-heyboer-usa-made-041318-125a1a
Note that it is listed for both the Tweed Deluxe and the Blackface but if you read the fine print it says
that the 5E3 Tweed used an 8K primary OT and this one is 6.6K. It is actually the Deluxe Reverb OT but
they say that it will work in the 5E3.
The one that I bought is also marked 041318 and 6.6K to 8 ohms but it was only $36 and it says made in Taiwan:
https://www.tubeaudiosupply.com/col...put-transformer-replacement-for-041318-125a1a
It arrived, and weighs 1.54 lbs which is middle of the road for a 20W OT.
Applied 122.5V in and got 4.37V out on the 8 ohm tap.
Turns ratio = 122.5/4.37 = 28.03
Imp ratio = 28.03^2 = 785.8
With an 8 ohm load = 6286 ohms
Primary DCR = 205.2 ohms
Secondary DCR = .8 ohms
These are much better than the Blues Jr OT
For the record the Blues Jr (actual Fender part) measures 14.9 oz = .93 lbs
And the Magnavox = 15 oz = .94 lbs
Note that this cheap Deluxe OT is about 1.5 times as heavy and might make a nice cheap Blues Jr OT upgrade.
I noticed on the Mojotone site that the 8K primary OT s for Marshall 18W amps and also those
for Vox amps are much heavier than most of the 15 to 20W Fender OT s. The Mojotone 7000218 for
example is called a British 18W 8K output transformer and is 2.5 lbs. It is not cheap at $77 currently
I've heard that Mojotone transformers are made by Heyboer and someone in the comments says
that this is the Heyboer 6135 18W, I also notice that the label on the OT says HT-6135.
The Mojotone OT for the Vox AC-15 is 2.28 lbs, also a good weight but 6K primary.
I might try the Mojotone 7000218 if we want to try a better 8K primary OT but then I have to wonder
if part of the 5E3 magic is from pushing the smallish OT.
I also stumbled onto this 8K pri, 25W OT on ebay: "OT19PP (USA) HC100 Output transformer 25VA - 8K
to 4/8/16 ohm for 18W Marshall" Stated as a 25W upgrade for the Marshall, it is 3"X3"X2.5" and 2.5lbs
for $70 claimed to be made in USA. Here's the description:
"This is a new 25VA Push-Pull model OT19PP Output transformer for tube guitar circuit applications (50Hz to 20KHz) using power tube pairs such as EL84 in a British Style Guitar amp such as the Marshall 18W using a larger lamination size (EI 1in) . This version of the transformer is built in USA to MPS custom design specs . I'm using audio grade EI-100 29M6 laminations as per origin Marshall OT size in a 1.125" oversized stack and bobbin wound construction. It's an interleaved winding with 8000 Ohm input impedance and three output impedances. In the HC100 end bells, this version is fully shielded."
Anyone know what the 29M6 lamination designation means?
The ebay seller is muzicalmatt has anyone dealt with him or have info on him?
I think that this and the Mojotone would make a nice upgrade for any of the Tweed 6V6 amps and the Princeton Reverb.
But, again, who knows how much of the tone if any comes from saturating the OT in those amps.
The comment on the Mojotone 7000218 also says that there are video clips comparing different 8K OT s and that this
one is a winner.
.
for Vox amps are much heavier than most of the 15 to 20W Fender OT s. The Mojotone 7000218 for
example is called a British 18W 8K output transformer and is 2.5 lbs. It is not cheap at $77 currently
I've heard that Mojotone transformers are made by Heyboer and someone in the comments says
that this is the Heyboer 6135 18W, I also notice that the label on the OT says HT-6135.
The Mojotone OT for the Vox AC-15 is 2.28 lbs, also a good weight but 6K primary.
I might try the Mojotone 7000218 if we want to try a better 8K primary OT but then I have to wonder
if part of the 5E3 magic is from pushing the smallish OT.
I also stumbled onto this 8K pri, 25W OT on ebay: "OT19PP (USA) HC100 Output transformer 25VA - 8K
to 4/8/16 ohm for 18W Marshall" Stated as a 25W upgrade for the Marshall, it is 3"X3"X2.5" and 2.5lbs
for $70 claimed to be made in USA. Here's the description:
"This is a new 25VA Push-Pull model OT19PP Output transformer for tube guitar circuit applications (50Hz to 20KHz) using power tube pairs such as EL84 in a British Style Guitar amp such as the Marshall 18W using a larger lamination size (EI 1in) . This version of the transformer is built in USA to MPS custom design specs . I'm using audio grade EI-100 29M6 laminations as per origin Marshall OT size in a 1.125" oversized stack and bobbin wound construction. It's an interleaved winding with 8000 Ohm input impedance and three output impedances. In the HC100 end bells, this version is fully shielded."
Anyone know what the 29M6 lamination designation means?
The ebay seller is muzicalmatt has anyone dealt with him or have info on him?
I think that this and the Mojotone would make a nice upgrade for any of the Tweed 6V6 amps and the Princeton Reverb.
But, again, who knows how much of the tone if any comes from saturating the OT in those amps.
The comment on the Mojotone 7000218 also says that there are video clips comparing different 8K OT s and that this
one is a winner.
.
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Here's another 8K pri 25W from the same ebay supplier but made in Mexico for $37:
OT20PP VC87 Output transformer 25VA & 8K/6K6 to 4/8/16 ohm
It is 2 lbs so a bit smaller than the OT19PP but larger than the Fender Tweed Deluxe OT.
OT20PP VC87 Output transformer 25VA & 8K/6K6 to 4/8/16 ohm
It is 2 lbs so a bit smaller than the OT19PP but larger than the Fender Tweed Deluxe OT.
M6 29 Gauge - 0.014" (0.355 mm) Grain Orientated Electrical Transformer Steel Lamination,
Grain-Oriented. This term is used to designate elec-
trical steels that possess magnetic properties which are
strongly oriented with respect to the direction of rolling.
By a process of rolling and annealing, alloys of suitable
composition can be produced with a metallic crystal
structure in which the grains are aligned so that mag-
netic properties are vastly superior in the direction of
rolling. This results in inferior properties in other direc-
tions, however.
By 1955, new oriented grades, M-7 and M-6, had
been developed and became the most widely used
grades of grain-oriented steel.
Designers now specify grain-oriented electrical steels,
such as M-2, M-3, M-4, M-6 and TRAN-COR H-0 and
H-1, for a large proportion of all distribution and power
transformers.
The reason for the intensive demand for grain-
oriented steel was the remarkable opportunity these
steels afforded to reduce the size of magnetic cores in
electrical apparatus, thereby also reducing the amount
of other materials required. Related factors that ex-
panded the application of this class of electrical steel
include the following:
a. Permeability at high flux densities is improved while
core loss is reduced. This is in contrast to the improve-
ment of nonoriented grades where core loss improve-
ments usually are accompanied by lower permeability
at high flux densities.
b. Power production and transmission economy war-
rant design of more efficient apparatus using better core
materials, especially with the increasingly heavy demand
for energy conservation through more energy-efficient
equipment.
c. With grain-oriented steel, the cost of the core gener-
ally is not increased, even though the price per unit
weight of core material is higher. In fact, the cost of a
transformer of suitable design and a given rating is nearly
always lower with grain-oriented steel.
d. Transformers with oriented steel cores are decidedly
smaller than those of the same rating made of conven-
tional silicon steel. This lowers handling cost and in-
creases the kva rating of distribution transformers that
can be mounted on a single utility pole. Oriented steels
also greatly increase the power rating of the largest
transformers that can be manufactured and shipped
economically.
For small laminated cores in which both the core loss
and permeability at high inductions are quite important,
a U-shaped lamination with very long legs cut parallel
to the rolling direction may make it feasible to use
Oriented M-6. Such shapes reduce the effects of joints
in the magnetic circuits. By making the cross-grain sec-
tion very short and up to 35% wider than the legs, the
relatively poor magnetic properties in this section of the
core and in the corners can be minimized.
https://www.brown.edu/Departments/Engineering/Courses/ENGN1931F/mag_cores_dataAKSteel-very good.pdf
https://edcorusa.com/en-ca/products/ei-187-m6-29-gauge-orientated-single-phase-steel-lamination
Let's start with the weighty issue first. The assumption is that you will get more for your money. But more of what? Often, but not always, a transformer is beefy because it utilizes a low grade of electrical steel. Transformer laminations come in a multitude of grades ranging from M6 to M55. The lower the number, the lower the core losses as measured in watts loss per pound of material. This is because the reluctance (the magnetic equivalent of resistance) of M6 is lower than the lesser grades with a higher number behind the "M". The higher the number, the higher the losses; there- fore, you must use more (all other things being equal) of MI 9 for a given VA (power) rating than if you use M6. As the number increases, the saturation point falls lower and lower. Even if you run Ml 9 at lower levels of flux density, magnetic distortion is still greater than for the more premium grades of laminations at the same operating level. Simply put, you must use more MI 9-to build our example transformer than you would need using M6 and your iron losses will be greater if all the other de- sign considerations are equal.
This is not meant to say that you should always reject a power transformer if it is heavy. Some power transformers built with M6 are heavy, and some transformers built with M19, M22, or M27 are designed to provide reasonable performance levels. The big mistake is to make decisions based solely on weight without knowing anything about the composite performance capabilities. We must know what the voltage regulation of the unit is, what temperature rise to expect, how current capacity was calculated, what flux density level the unit runs at, etc. Just don't buy on weight alone since it might indicate cost constraints imposed by the manufacturer (Ml 9 and M27 cost 40% to 70% less than M6) and a heavy unit may have poor overall performance characteristics.
https://www.enjoythemusic.com/magazine/sound_practices/1/core_issue.htm
Grain-Oriented. This term is used to designate elec-
trical steels that possess magnetic properties which are
strongly oriented with respect to the direction of rolling.
By a process of rolling and annealing, alloys of suitable
composition can be produced with a metallic crystal
structure in which the grains are aligned so that mag-
netic properties are vastly superior in the direction of
rolling. This results in inferior properties in other direc-
tions, however.
By 1955, new oriented grades, M-7 and M-6, had
been developed and became the most widely used
grades of grain-oriented steel.
Designers now specify grain-oriented electrical steels,
such as M-2, M-3, M-4, M-6 and TRAN-COR H-0 and
H-1, for a large proportion of all distribution and power
transformers.
The reason for the intensive demand for grain-
oriented steel was the remarkable opportunity these
steels afforded to reduce the size of magnetic cores in
electrical apparatus, thereby also reducing the amount
of other materials required. Related factors that ex-
panded the application of this class of electrical steel
include the following:
a. Permeability at high flux densities is improved while
core loss is reduced. This is in contrast to the improve-
ment of nonoriented grades where core loss improve-
ments usually are accompanied by lower permeability
at high flux densities.
b. Power production and transmission economy war-
rant design of more efficient apparatus using better core
materials, especially with the increasingly heavy demand
for energy conservation through more energy-efficient
equipment.
c. With grain-oriented steel, the cost of the core gener-
ally is not increased, even though the price per unit
weight of core material is higher. In fact, the cost of a
transformer of suitable design and a given rating is nearly
always lower with grain-oriented steel.
d. Transformers with oriented steel cores are decidedly
smaller than those of the same rating made of conven-
tional silicon steel. This lowers handling cost and in-
creases the kva rating of distribution transformers that
can be mounted on a single utility pole. Oriented steels
also greatly increase the power rating of the largest
transformers that can be manufactured and shipped
economically.
For small laminated cores in which both the core loss
and permeability at high inductions are quite important,
a U-shaped lamination with very long legs cut parallel
to the rolling direction may make it feasible to use
Oriented M-6. Such shapes reduce the effects of joints
in the magnetic circuits. By making the cross-grain sec-
tion very short and up to 35% wider than the legs, the
relatively poor magnetic properties in this section of the
core and in the corners can be minimized.
https://www.brown.edu/Departments/Engineering/Courses/ENGN1931F/mag_cores_dataAKSteel-very good.pdf
https://edcorusa.com/en-ca/products/ei-187-m6-29-gauge-orientated-single-phase-steel-lamination
Let's start with the weighty issue first. The assumption is that you will get more for your money. But more of what? Often, but not always, a transformer is beefy because it utilizes a low grade of electrical steel. Transformer laminations come in a multitude of grades ranging from M6 to M55. The lower the number, the lower the core losses as measured in watts loss per pound of material. This is because the reluctance (the magnetic equivalent of resistance) of M6 is lower than the lesser grades with a higher number behind the "M". The higher the number, the higher the losses; there- fore, you must use more (all other things being equal) of MI 9 for a given VA (power) rating than if you use M6. As the number increases, the saturation point falls lower and lower. Even if you run Ml 9 at lower levels of flux density, magnetic distortion is still greater than for the more premium grades of laminations at the same operating level. Simply put, you must use more MI 9-to build our example transformer than you would need using M6 and your iron losses will be greater if all the other de- sign considerations are equal.
This is not meant to say that you should always reject a power transformer if it is heavy. Some power transformers built with M6 are heavy, and some transformers built with M19, M22, or M27 are designed to provide reasonable performance levels. The big mistake is to make decisions based solely on weight without knowing anything about the composite performance capabilities. We must know what the voltage regulation of the unit is, what temperature rise to expect, how current capacity was calculated, what flux density level the unit runs at, etc. Just don't buy on weight alone since it might indicate cost constraints imposed by the manufacturer (Ml 9 and M27 cost 40% to 70% less than M6) and a heavy unit may have poor overall performance characteristics.
https://www.enjoythemusic.com/magazine/sound_practices/1/core_issue.htm
@Printer2 Thanks for all the excellent info, I'm going to have to read it a few times.
I understand that weight alone is not the best indicator but it is a start and if we knew that
most were using similar materials then it would be somewhat valid.
I suppose the best thing would be to measure LF distortion vs. power input.
LF should be easy and there's probably a PC sound card app that would work good enough.
I've used ARTA in the past for distortion measurements. Oh, forgot that a high voltage, low
distortion drive source is needed.
A simple way to do this would be to drive the 8 ohm side from a high quality SS amp and put
a resistive high power load on the secondary, then resistively divide it down to line level for
input to a sound card. I'd think that driving it backwards is still fairly valid.
High frequency response and distortion, I think, would be an indicator of the quality of
construction, interleaving etc. Not sure if it is valid to do this driving it backwards.
I understand that weight alone is not the best indicator but it is a start and if we knew that
most were using similar materials then it would be somewhat valid.
I suppose the best thing would be to measure LF distortion vs. power input.
LF should be easy and there's probably a PC sound card app that would work good enough.
I've used ARTA in the past for distortion measurements. Oh, forgot that a high voltage, low
distortion drive source is needed.
A simple way to do this would be to drive the 8 ohm side from a high quality SS amp and put
a resistive high power load on the secondary, then resistively divide it down to line level for
input to a sound card. I'd think that driving it backwards is still fairly valid.
High frequency response and distortion, I think, would be an indicator of the quality of
construction, interleaving etc. Not sure if it is valid to do this driving it backwards.
This thread, for me anyway, has become more about output transformers.
We got a Fender Excelsior PP6V6GT with another example OT, it is the same size as the Fender Blues Jr but
has end bell covers so I'd guess that the weight without the covers would be the same roughly .9 lbs.
It is very small.
This is the strangest "modern" (2013) Fender amp that I've ever seen, it is in the Pawn Shop series and is intended
to be like something you might find in one. Looks like it might be from the 1940s and has a two chassis
design with PP 6V6GT s and a 15" speaker. There are reports that it was $300 new and a lot of tube amp for the money.
Applied 121.6V on the primary and got 3.78 out on the 8 ohm tap
Turns ratio is 121.6/3.78 = 32.17
Impedance ratio 32.17^2 = 1034.91
For and 8 ohm load, primary = 8279 ohms
Primary DCR is 300 ohms, Red to Blue = 150.5 Red to Brown = 149.5 ohms
Secondary = .35 ohms
We got a Fender Excelsior PP6V6GT with another example OT, it is the same size as the Fender Blues Jr but
has end bell covers so I'd guess that the weight without the covers would be the same roughly .9 lbs.
It is very small.
This is the strangest "modern" (2013) Fender amp that I've ever seen, it is in the Pawn Shop series and is intended
to be like something you might find in one. Looks like it might be from the 1940s and has a two chassis
design with PP 6V6GT s and a 15" speaker. There are reports that it was $300 new and a lot of tube amp for the money.
Applied 121.6V on the primary and got 3.78 out on the 8 ohm tap
Turns ratio is 121.6/3.78 = 32.17
Impedance ratio 32.17^2 = 1034.91
For and 8 ohm load, primary = 8279 ohms
Primary DCR is 300 ohms, Red to Blue = 150.5 Red to Brown = 149.5 ohms
Secondary = .35 ohms