New 5F4 build-transformers

[Travst]

Hi all, first post here after lurking for a time.

I picked up a nice tweed cab in a trade and a 5F4 Victoria chassis on Ebay. My parts will be arriving over the next few days to start this build. With regard to transformers, I'm looking at the Magnetic Components Tweed Bassman set from Triode:

Fender Tweed Bassman Transformer Bundle

I want to make certain I've made the correct choice before ordering. Do these fill the bill? If anyone's used them, how do you like them? The reviews seem very positive here and elsewhere.

John

[JoeM]

Are you doing an exact copy of the 5F4 power supply? The 5F6A has the choke in a different location, (like other later Fenders), but the 5F4 has it earlier in the PS. You might contact Triode and see if they carry the larger choke.

I used the choke in that set in my 5F6A clone, and have used a Magnetics Components OT for a DR in my Princeton. Very happy with them, and Triode was a great company to deal with.

[Travst]

Joe, I should have specced which layout I'm using. I'm going by the Ceriatone layout in general. Thanks for the tip, I'll talk to Triode about the choke.

http://ceriatone.com/images/layoutPi...one_100508.jpg

John

[ThermionicScott]

The bassman iron should work, but i think the original Supers had smaller iron. If that a consideration.

[Tom Phillips]

The bassman iron should work, but i think the original Supers had smaller iron. If that a consideration.

Yes a significant difference is the smaller OT used in the Super. Here are a couple of comparison photos.
Both models sound great. The Magnetic Components OT has a multiple impedance secondary which is nice.

[Travst]

Yes a significant difference is the smaller OT used in the Super. Here are a couple of comparison photos.
Both models sound great. The Magnetic Components OT has a multiple impedance secondary which is nice.

Yes, I thought the Supers had smaller iron as well, but MC seems to recommend the 40/50 watt transformers. I wouldn't mind finding a match in the MC line that's a lighter wattage. Any recommendations? I'm using 2x12" speakers at 8 ohms, so only the 4 ohm impedance is absolutely necessary.

[Tom Phillips]

Yes, I thought the Supers had smaller iron as well, but MC seems to recommend the 40/50 watt transformers. I wouldn't mind finding a match in the MC line that's a lighter wattage. Any recommendations? I'm using 2x12" speakers at 8 ohms, so only the 4 ohm impedance is absolutely necessary.

It’s really your call about what you want to build. As has been mentioned above, the transformer set will work except the choke may be underrated since the Super places the choke in the power tube plate supply where the current is highest. The choke needs to be rated for higher current or you will experience excessive sag and eventually failure of the choke. You could move the choke to the screen supply and it should work fine. However, now you are deviating from the 5F4 design. If your goal is to build an exact clone of a 5F4 super then it’s a different story and you would probably need to locate individual transformers from specialty sources. Total cost would be much higher. I took a quick look but I did not see an exact match for the 5F4 in the MC line.

If you build with the proposed transformer bundle & mods you will still have a nice sounding amp and you will get a little more power because of the PT & OT upsize. The bundle price is good and MC quality is excellent. The 40/50 watt transformer set is just what they have settled on to satisfy the need for several amps.

The Ceriatone layout does not include screen resistors. If you really like to crank your amp into power amp distortion I recommend that you add them to your build.

And now a little rant about the Ceriatone supplied layout:
The cookie cutter copying of old circuits leaving out improvements such as the screen resistors is just dumb. It demonstrates that the people running these companies do not understand the technical aspects of what they are doing. I suppose that’s OK as long as they don’t claim otherwise and you can participate in this forum for technical advice.
End rant.

The 5F4 Super was designed at a time when the tubes were cheap and generally higher quality and, most importantly, when the amps were played clean. Fender soon added the classic 470Ω screen resistors to their designs. You can do that too. 1kΩ / 5W screen resistors would be even better. Their purpose is to reduce the steep rise in screen power dissipation that occurs when the power tubes are driven into distortion.

Regards,
Tom

[Travst]

Excellent points, Tom and good advice that I'll take note of. I have read quite a few threads that agree with your thoughts and it makes perfect sense to me to add improvements. I'm not locked into the 'stock' design' by any means. I'll take the time to read up on screen resistors. I've built an 18 watt, modded a couple of VJs and fixed several amps. It's all a learning experience to me right now, but the way for me to 'get' things is to dive in and do it and ask for advice from those who know much more. The point about the choke is well taken, and I'll see if Triode can provide the package with a choke for the higher current.

[ThermionicScott]

Good catch, Tom. The choke in that kit is only rated for 90mA. Not enough for a strict 5F4 implementation -- the #14684 type Weber ships with the 5F4/5e5/5e7 kits is rated for 200 or so.

[Travst]

I have a chance to buy some Ballantine transformers from an old theater amp. The specs are as follows:

Power Transformer
Black= Common Primary
Red/black= 120volt Primary
Yellow/black= 125volt Primary
Green/black= 135volt Primary

Green and Green/yellow= 6.3 volt Center tapped heater
Blue and Blue/yellow= 24 volt Center tapped
Red and Red/yellow= 630 volt Center tapped
Yellow= 64 volt tap.

Output Transformer
Blue, and brown= the plate taps
Red= center tap of the plate taps
Yellow= 8 ohm tap
Green= 16 ohm tap
Black= ground or common

The amp had a tube complement very similar to my Super, but the 630v compares to 680v on the Ceriatone layout. Is this suitable for a Super, and are these considered to be good transformers?

John

[ThermionicScott]

That PT sounds good. You'd need to fiddle with the bias supply to get the right voltage, but it's better to have too much available than not enough!

If this was an old cathode-biased amp with a high-value dropping resistor before the screen supply, the primary impedance of the OT may be too high. This wouldn't be the end of the world in your Super, but it would rob some power. There are ways to measure the impedance ratio of a transformer.

- Scott

[Travst]

Thanks, Scott. These seem like nice units, so I'll see if I can make them mine.

John

[Travst]

After buying the Ballentine transformers described above, I have been slowly working on this project, but got sidetracked for a while with a TDPRI competition guitar build. I have the board all wired up and the chassis all prepped, and realized that the PT doesn't have 5w leads for the 5U4G rectifier heaters. It looks like the Weber WU4GB copper cap would substitute for the 5U4G. It looks like that's my only option unless anyone can think of a solution. Also, if I use the cap, would pins 8 and 2 on the cap be wired together, and then a wire run to the standby switch? There are some posts that indicate my B+ will rise a bit due to the copper cap, but since I'm starting out with slightly lower voltage that the Ceriatone layout above, would that work out?

Weber's schematic:

https://taweber.powweb.com/store/5f4_schem.jpg

[ThermionicScott]

D'oh, I didn't catch that there wasn't a 5V winding! (That must be some old iron.) You won't need to wire anything to pin #2 on the rectifier socket. The WU4 should come close enough in voltage for your needs -- you can always pick up other Copper Caps (like the WR4, WY3, and WZ34) if you want to fine-tune the B+.

- Scott

[Travst]

Thankee, Scott. Obviously, I didn't catch it either. As for the choke, I settled on the Heyboer from Weber... 5-8H @ 200ma, 125 ohm.