JTM45 Build with 6L6's, diode bridge in to replace GZ34

[Matador]

If the tubes can take the extra plate voltage, don't sweat it.

Keep in mind most 6L6GC's spec the maximum plate voltage in pentode operation at 500VDC, so running at 530V+ isn't conducive to long tube life (although it likely would work, at least for a while).

 

[Spencerleehorton]

I have opted to try some 6P3S tubes and for rectifier I have several 5U4GB.
Will get proper mains txf but will try this output txf from the line 6 spider.

 

[Spencerleehorton]

Using the 5u4 rectifier tube can I have a lower mains transformer output?
I have an option to get a mains txf with 580v ct, so 2 x 290v rather than the 2 x 350v.
I wondered what the result would be?

 

[Accelerator]

The “best bet” for me is that you can go for the Marshall 1974X 18-watter with Tremolo and EZ81/6CA4 Rectifier Tube if you are a “bedroom player” – small gig-er or you can go for the legendary Marshall 1962 “Bluesbreacker” 35-watter that Eric Clapton used for the:

“John Mayall and the Bluesbreackers feat. Eric Clapton” ~ “Beano” Recording sessions

https://www.fuzzfaced.net/bluesbreaker-marshall.html

With GZ34 rectifier Tube and Tremolo…

The reason that I prefer these Rectifier Tube Amps, over the more efficiency “silicon solid state bridges” amps, is that when you “break them up high”, you will have got this beautiful “Sag” from the Rectifier Tubes that no Compression Unit can give it to you, so if you use these Marshall Rectifier Amps for recordings, it is a win-win situation…

 

[Matador]

The reason that I prefer these Rectifier Tube Amps, over the more efficiency “silicon solid state bridges” amps, is that when you “break them up high”, you will have got this beautiful “Sag” from the Rectifier Tubes that no Compression Unit can give it to you, so if you use these Marshall Rectifier Amps for recordings, it is a win-win situation…

You can simulate a tube rectifier with a silicon rectifier and a 47-100 ohm power resistor, and get all of the benefits of longevity and robustness of the silicon rectifier with the sag of the tube rectifier.

I've repaired/replaced enough tube rectifiers to ever consider putting on in a custom build.

 

[Accelerator]

You can simulate a tube rectifier with a silicon rectifier and a 47-100 ohm power resistor, and get all of the benefits of longevity and robustness of the silicon rectifier with the sag of the tube rectifier.

I've repaired/replaced enough tube rectifiers to ever consider putting on in a custom build.

Yes, I know this Matador…

Ted Weber (R.I.P.) of the Weber VST has done that back in time with his “Tube rectifier simulators” that his sold, but it is just that, a “simulation” not the real “sag” that a real rectifier tube can gives you…

In particular music genres like 50’s blues, 60’s blues rock which specifically the Authenticity of the real “feeling” it is what we are looking for, nothing can beat the real thing…

Now, if you would like to put some kind of “protection” to the rectifier tube, and get all of the benefits of longevity and robustness of the silicon rectifier with the sag of the tube rectifier, you can put 2 silicon diodes at the anodes of the rectifier tube and connect these 2 silicon diodes with your P.T. AC H.T., something that Ceriatone Amplification do, to Ceriatone Amplification Tube Rectified Amplifiers clones which he makes...

 

[Spencerleehorton]

ive ordered one of these for the mains transformer

https://modulusamplification.com/jt...sformer-with-clamp-bracket-mod0002-3136-p.asp

the schematic i'd like to work off now is this one

https://mhuss.com/Plexi6V6/Plexi6V6.gif

on the schematic it details using a hammond mains txf which is 620VCT @ 115ma

mine is going to be slightly higher than that at 690VCT @ 150ma

if i use a 4.5k 5watt resistor just after the standby switch it should drop me down to the required 443v at the A node.

hopefully ive got that right but wanted to check before i start!!

 

[Matador]

Isn't that essentially a 345-0-345 configuration? With a full wave rectifier, that would put you at ~485V which isn't too far off of your 450V target.

 

[Tubetec]

4.5k in series with the HT line sounds really high to me , 450 ohms sounds more like it but even at that it will seriously effect how the amp handles peaks .
The resistor might also end up dissipating signifigantly more heat than you expect , Id say a 5 watt component will go up in a puff of smoke in no time .

I meant to reply earlier to this thread , but I forgot until it resurfaced ,

 

[Tubetec]

Its true rectifier tubes can go out in a bad way where mains transformer is at risk ,
When you had good quality GZ34's it wasnt so much of a problem ,
now its a very different story ,
Sovtek 5AR4/GZ34 was my 'ould reliable' for years after the Mullards became non obtainable for reasonable money . I turned away a few customers over the years who wanted JJ's Ruby's or other Shenzen crap fitted .
Thats something that could come back and take a serious bite out of your ass pocket .

 

[john12ax7]

Check with the manufacturer. Transformers are often speced unloaded, so a 345-0-345 might end up around 450V under load.

 

[Accelerator]

@Spencerleehorton​

With the JTM45 Vintage Style Power Transformer with Clamp Bracket MOD0002 for Full Wave Two-Phase Rectification you will have:

V (Peak) D.C. = 0.71 X Sec. V A.C. = V (Peak) D.C. = 0.71 X 690 V A.C. = V (Peak) D.C. = 489,9 DC Volts

V (Avg) D.C. = 0.45 X Sec. V A.C. = V (Avg) D.C. = 0.45 X 690 V AC = V (Peak) D.C. = 310,5 DC Volts

I D.C. = 1.00 X Sec. I A.C. = I D.C. = 1.00 X 150mA = I D.C. = 150mA

Now you will have several thinks and facts to consider...

489,9 DC Volts or even 450 DC Volts it is way too high for any “average” New Sensor Production (Sovtek) 6V6GT tubes and only the JJ Electronic 6V6S from the current production tubes have the ability to withstand such high voltages…

As I always said to everyone:

“Before you starting everything, especially a tube amplifier project, you have to educate yourself from better makers than you, so you will be not as newbie as a newb and at least don’t be as cheapie as a cheap, because you will ended up with a problematic crappie as a crap amplifier…

The education today it is the only free thing that you can have to do…”

So, here with these articles about Rectifiers & Smoothing and Filtering the Power Supply you can have same good “food for thoughts” for free by the British valve amplifier designer MCs Merlin Blencowe aka The Valve Wizard and I high recommend you to buy and read his books:

Designing Tube Preamps for Guitar and Bass, 2nd edition

&

Designing Power Supplies for Valve Amplifiers

As I wrote before:

In particular music genres like 50’s blues, 60’s blues rock which specifically the Authenticity of the real “feeling” it is what we are looking for, nothing can beat the real thing (the rectifier tube, in our case the 5AR4/GZ34 …)

Now, if you would like to put some kind of “protection” to the rectifier tube, and get all of the benefits of longevity and robustness of the silicon rectifier with the sag of the tube rectifier, you can put 2 silicon diodes at the anodes of the rectifier tube (to do the hard work…) and connect these 2 silicon diodes with your P.T. AC H.T., something that Ceriatone Amplification do, to Ceriatone Amplification Tube Rectified Amplifiers clones which he makes and Merlin Blencowe recommends...

 

[Spencerleehorton]

Yes your so right, I’ll stick with the tube rectifier, my only change I was entertaining was because my drummer was moaning on the last gig my 50 watt plexi was too loud on stage and he couldn’t hear his cymbals!!
I was only at 10 o’clock volume and my PPIMV was up full with my 68 plexi?
It was on a big stage in a 500+ people size marquee!!
The Ceriatone layout I’ll stick too as it does have a half volume switch.
I’ll get reading again as well!!

 

[Spencerleehorton]

How would a 5u4gb fair?

 

[Accelerator]

@Spencerleehorton​

How would a 5u4gb fair?

The 5U4-GB Rectifier tube has bigger “sag” but it demands 5 volt / 3 A for the operation, something that no-one common JTM45 Power Transformer in the market can give you, as the most of them ends up to 5 volts / 2 A for the GZ34 Rectifier tube…

You –may- can have a Custom JTM45 Power Transformer by Mercury Magmetics with 5 volt / 5 A for the 5U4-GB Rectifier tube operetion, like the P4550JT-G2 or the P4550JT-G2M but in this case the price of these P.T. s will go astronomical high at $333 …

 

[Spencerleehorton]

Yeah just wanted to check that!!
GZ34 it is!!

 

[Spencerleehorton]

My next question would be is it ok to use 5881 tubes or 6P3P tubes?
For the Ceriatone layout?

 

[Matador]

The Ceriatone layout is talking about "star grounds" so I immediately want to ignore it.

A 5881 should work fine in that circuit.

 

[Accelerator]

@Spencerleehorton​

My next question would be is it ok to use 5881 tubes or 6P3P tubes?
For the Ceriatone layout?

Just to put it “straight & clear”, in this Fender Bassman 5F6-A / Marshall JTM 45 topology you can use any of the well-known Power Tubes that you like…

It is not the circuit (which in both cases it is nearly intertidal as Jim Marshall coped Leo Fender’s Bassman 5F6-A schematic…), but the Radiospades Output Transformer impendence, the (high gain) ECC83 Pre-Amp. tubes and the KT-66 Power tubes that makes the Marshall JTM45 amp. to sound so “Marshall-y”…

Now, If you reverced it and use the 12AY7 pre-amp. tubes (which were the “original” pre-amp. tubes that the Fender Bassman 5F6-A was designed) and make the proper JEDEC 7AC basing for the 5881 Power Tubes and connect them at the 6.600 tap of the Radiospades Output Transformer, you will have sound wise a “Fender Bassman 5F6-A amplifier” rather than a Marshall JTM 45 amp…

 

[Spencerleehorton]

Another question that springs to mind is how to do the heater wires, there seems to be some difference of opinion in wether to twist them and have them 90 degrees to other wires or have them come in from above and be in parallel next to each other which is claimed to be better to reduce noise!
I wondered what your opinion was?