Homemade 5F2A Tweed Princeton amp, first build

SG John said:
Also, if any of you have a preference for transformers, let me know. What is the best modern equivalent to a Radio Spares or early Drake? How are the modern Hayboer trannies? Are the Classic Tone trannies any good? I'd like to know sooner than later.

Cheers! :cheers:
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I second the vote for Merren Audio. I have Merren iron in my '69 Superlead build & am glad I got them. Also have a Merren OT (Marstran/Heyboer PT) in my JTM50 build.
The Merren RS OT is the only one built with turret/tag board terminals like the original RS OT had15815703000634762499399813231491.png
Cheers
Edit: If you want to do it "right" with regards to the chassis etc, chase up some of the McMurdo octal sockets as used in the originals. You can source them from PM Components, Sittingbourne, UK. They have an eBay site. Cheers
 
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Request for a quote for output and power transformers was sent to Merren Audio.

I also requested info from the Tube Depot regarding their chassis. Still have not heard back.

I'll probably go with Valvestorm, as I'll be needing some other stuff off of the checklist, and you get a price break when you buy the chassis and panels together.

What choke should I use?

Valvestorm.com has the Mercury Magnetics on their website. In looking for information on Marshall chokes, it looks like I should be running a Magnetic Components 40-18058 choke. It is a 250 mA, 3 Hy choke, and can take the power loads of a KT66, and not overheat. It looks like a normal choke for EL34 would by a 20 Hy choke. The Mercury Magnetics choke on Valvestorm is 7 Hy.
 
SG John said:
What choke should I use?

Valvestorm.com has the Mercury Magnetics on their website. In looking for information on Marshall chokes, it looks like I should be running a Magnetic Components 40-18058 choke. It is a 250 mA, 3 Hy choke, and can take the power loads of a KT66, and not overheat. It looks like a normal choke for EL34 would by a 20 Hy choke. The Mercury Magnetics choke on Valvestorm is 7 Hy.
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Im not aware of Marshall ever using a 7 Henry Choke, well not during the "classic Marshall" years anyway. It was either an RS 20Hy/690 ohm that was used on a good many JTM45's & a few JTM50's, or a (C1999) 3Hy/110 ohm that was used on JTM45's & all classic Marshalls. There were also some "black box" choked JTM45's, but I don't know the specs of this choke, or where you'd find a repro.
So which one to use is up to you. Be aware though that the amp will feel & react differently depending on which choke you use. Cheers
Edit: I have used Heyboer, Marstran/Heyboer & Classictone chokes. I usually don't go for the Classictone transformers, but have had no problem with their filter chokes. Cheers
 
Personally, if doing a JTM45, I would go for the RS 20Hy, 70mA, 690 ohm type filter choke. It was the most common choke used in JTM45's. You could ask Chris Merren about one, pretty sure he'll be able to supply it, or source elsewhere. Just make sure the specs are correct, as given above. Cheers
 
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syscokid said:
:what:

Or... Get all your trannies from Marstrans and ask Brian Wallace on which choke. He sells a 3H and a 20H
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Merren Audio do supply filter chokes, they are not listed on his site though.
Brian Wallace is very knowledgeable about all things Marshall & the Marstran/Heyboer iron are good products.
The Classictone filter chokes I have used are wound on a paper former like the early originals were, the Marstran on a plastic bobbin (like the "later" Drake originals). Paper former or plastic bobbin doesn't make an audible difference when it comes to filter chokes though. The Classictone chokes do cost a bit less than others. Cheers
 
ivan H said:
Merren Audio do supply filter chokes, they are not listed on his site though.
Brian Wallace is very knowledgeable about all things Marshall & the Marstran/Heyboer iron are good products.
The Classictone filter chokes I have used are wound on a paper former like the early originals were, the Marstran on a plastic bobbin (like the "later" Drake originals). Paper former or plastic bobbin doesn't make an audible difference when it comes to filter chokes though. The Classictone chokes do cost a bit less than others. Cheers
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How do the Merrens compare in price to the Marstrans?
 
syscokid said:
How do the Merrens compare in price to the Marstrans?
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I have not bought a filter choke off Chris (I have seen pics of them used on others builds). His transformers cost a little more than others, but his products are very good. You get what you pay for. His Marshall OT's are the best sounding replicas I have heard, especially the C1998 in my '69 superlead build. Cheers
 
ivan H said:
I have not bought a filter choke off Chris (I have seen pics of them used on others builds). His transformers cost a little more than others...
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"Others"? More than Marstrans? More than Mercury Magnetics?

Classic Tone is very affordable and still very good quality. Marstrans are twice the price, but excellent Heyboer-built quality. Mercury Magnetics are quite a bit more expensive than Marstrans, but IMO the MMs are overpriced compared to the Marstrans.
 
syscokid said:
"Others"? More than Marstrans? More than Mercury Magnetics?

Classic Tone is very affordable and still very good quality. Marstrans are twice the price, but excellent Heyboer-built quality. Mercury Magnetics are quite a bit more expensive than Marstrans, but IMO the MMs are overpriced compared to the Marstrans.
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They do cost more than Marstran. I'd need to go back & look through Merren Audio invoices, then look at prices on the MM site to know for sure how those compare. Cheers
 
ivan H said:
I second the vote for Merren Audio. I have Merren iron in my '69 Superlead build & am glad I got them. Also have a Merren OT (Marstran/Heyboer PT) in my JTM50 build.
The Merren RS OT is the only one built with turret/tag board terminals like the original RS OT hadView attachment 38328
Cheers
Edit: If you want to do it "right" with regards to the chassis etc, chase up some of the McMurdo octal sockets as used in the originals. You can source them from PM Components, Sittingbourne, UK. They have an eBay site. Cheers
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Those look PURRRRRRRTY...
Never used them before, but they sure look like a nice transformer. Three alien thumbs up !!!
 
Radio Spares JTM45 choke 10uH 150ma. That was the replacement for my 1963 JTM45 back in the 1980's it did not change the sound any.
I don't think you can get that choke anymore.
I find this interesting on the Tweed Bassman 100K slope resistor. Every Hendrix owned Marshall I have seen photos of or in real life
used a 33K slope resistor. Stock 56K lead 47K bass so they say.

 
67plexi said:
Radio Spares JTM45 choke 10uH 150ma. That was the replacement for my 1963 JTM45 back in the 1980's it did not change the sound any.
I don't think you can get that choke anymore.
I find this interesting on the Tweed Bassman 100K slope resistor. Every Hendrix owned Marshall I have seen photos of or in real life
used a 33K slope resistor. Stock 56K lead 47K bass so they say.

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Cool info from that video. Will the real Bassman please stand up...!
 
Yes, cool video, thanks for posting. The resistor paralleling the pot to ground, as on the middle & presence pot, is a common way to "adjust" the value of the pot that is higher in value than what you need. For pots that "aren't" grounded, like the treble & bass pots, the resistor can be simply put across the pot (across the two "outside" terminals). Whether the resistor is "to ground" or "across the two outside terminals", it will alter the pots "taper". Cheers
 
67plexi said:
Radio Spares JTM45 choke 10uH 150ma. That was the replacement for my 1963 JTM45 back in the 1980's it did not change the sound any.
I don't think you can get that choke anymore.
I find this interesting on the Tweed Bassman 100K slope resistor. Every Hendrix owned Marshall I have seen photos of or in real life
used a 33K slope resistor. Stock 56K lead 47K bass so they say.

Click to expand...


Thanks for posting that Steve. Does the same information hold true for a JTM45? SHould I be looking at the types of pots, whether they are audio taper or linear? Also the values of the slope resistors and the tail resistor on the phase inverter? Or should I stick with the Marshall schematic?
 
SG John said:
Thanks for posting that Steve. Does the same information hold true for a JTM45? SHould I be looking at the types of pots, whether they are audio taper or linear? Also the values of the slope resistors and the tail resistor on the phase inverter? Or should I stick with the Marshall schematic?
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Ha ha… SG John has got the FEVER... :woohoo:

i-got-a-fever-snl.jpg

And the solution is to build more amps!
 
SG John said:
Does the same information hold true for a JTM45? SHould I be looking at the types of pots, whether they are audio taper or linear? Also the values of the slope resistors and the tail resistor on the phase inverter? Or should I stick with the Marshall schematic?
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For pots, I use "Audio taper" for the volume & bass controls & "Linear" for the treble, middle & presence controls. Some do like to use an Audio taper pot for the treble control too, though the schematic usually calls for a Linear.
I would recommend metering the pots to make sure none are below the stated value.
Maybe try the "stock" values for the slope resistor (56k for a JTM45) & the PI tail resistor first. You can easily change them out later if you want to. Cheers
 
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