Guitar Amp build suggestions

Help Support GroupDIY:

Potato Cakes

Well-known member
Joined
Jul 1, 2014
Messages
1,876
Location
Nashville, TN
The first obstacle, and probably the biggest one at this point, is the power transformer. Ideally, I would like one transformer to supply B+ and dual filaments like in the schematic, but since I am looking for the secondary voltage to be in the 200-230VAC range, it limits what is available that has three secondary windings outside a custom order. Most of these transformers are CT, so my question is couldn't I just use one side of the of the high voltage winding and the CT as my VAC connections to the rectifier and cap off the other side of the HV winding? Would I also then half my current rating for that winding? If so, this would make something like the Hammond 369KX perfect for what I'm after as it has 300mA for the HV winding, and even half of that would be enough for B+ voltages required by two 12AX7s and two EL84s. I can always use a second transformer if necessary but would like to avoid needing to do so.

Thanks!

Paul
 

Potato Cakes

Well-known member
Joined
Jul 1, 2014
Messages
1,876
Location
Nashville, TN
Matador said:
Antek torroidal? Most of them have quad secondaries.

https://www.antekinc.com/content/AS-05TC200.pdf

I completely forgot out those guys. That transformer is perfect. Except it doesn't have the vintage paper laminate the oozes with vibe, tone, unicorns, etc. But I suppose I could compromise a little to get the exact voltages without having to engage in unnecessary funny business with electrons.

Thanks!

Paul
 

Matador

Well-known member
Joined
Feb 25, 2011
Messages
2,047
Location
Bay Area, California
I bet if you called them up, and asked them if it could be licked by a unicorn, they would happily let you pay $100 more for it. :)

Antek's seem really well made, and they have many dozen's of configurations.  At a $30 price point, it's not even out of the question to have several of them in a single project without breaking the bank.

 

Potato Cakes

Well-known member
Joined
Jul 1, 2014
Messages
1,876
Location
Nashville, TN
Matador said:
I bet if you called them up, and asked them if it could be licked by a unicorn, they would happily let you pay $100 more for it. :)

Antek's seem really well made, and they have many dozen's of configurations.  At a $30 price point, it's not even out of the question to have several of them in a single project without breaking the bank.

Indeed. Thanks again for reminding me about these guys. Can't beat that price.

Thanks!

Paul
 

john12ax7

Well-known member
Joined
Oct 14, 2010
Messages
1,845
Location
California, US
Hammond offers a wide variety of transformers in varying plate voltages.  You can get them at places like Antique Electronic Supply.
 

Potato Cakes

Well-known member
Joined
Jul 1, 2014
Messages
1,876
Location
Nashville, TN
john12ax7 said:
Hammond offers a wide variety of transformers in varying plate voltages.  You can get them at places like Antique Electronic Supply.

I looked at Hammond first. Outside of a custom job I would have to do the V-CT connection that I mentioned above. I think the Antek option will work very well.
 

Potato Cakes

Well-known member
Joined
Jul 1, 2014
Messages
1,876
Location
Nashville, TN
Just ordered an unfinished 1x10 cabinet for a Vibro Champ and a matching chassis with component cut outs for that amp, which has the same number of tubes for the Spitfire, all for about $300 shipped. I'll do a separate thread for building an post its progress once I start on it.

Thanks!

Paul
 

john12ax7

Well-known member
Joined
Oct 14, 2010
Messages
1,845
Location
California, US
Potato Cakes said:
I looked at Hammond first. Outside of a custom job I would have to do the V-CT connection that I mentioned above. I think the Antek option will work very well.

I'm not sure why you would only use half the secondary.  Guitar amps usually use half wave rectifiers. Something like 400 VCT would give you around 250 V B+ with a tube rectifier.
 

Potato Cakes

Well-known member
Joined
Jul 1, 2014
Messages
1,876
Location
Nashville, TN
john12ax7 said:
I'm not sure why you would only use half the secondary.  Guitar amps usually use half wave rectifiers. Something like 400 VCT would give you around 250 V B+ with a tube rectifier.

Going off of the schematic I'm using it shows 285VAC on the secondaries and it's putting out 352VDC. So for this circuit I would need to lower the secondary voltage to get the B+ to the level to suit my needs.

Thanks!

Paul
 

john12ax7

Well-known member
Joined
Oct 14, 2010
Messages
1,845
Location
California, US
It's 285V on each side of the ct.  They are using a 570 VCT transformer to get 352 VDC.  So yes scale it down,  but still use the full secondary.
 

Potato Cakes

Well-known member
Joined
Jul 1, 2014
Messages
1,876
Location
Nashville, TN
john12ax7 said:
It's 285V on each side of the ct.  They are using a 570 VCT transformer to get 352 VDC.  So yes scale it down,  but still use the full secondary.

I cannot read. I am also an idiot, once again. You, of course, are right. That will make things even easier.

I still can't believe I missed that. I must have picked a bad day to quit smoking...

Thanks!

Paul
 

Tubetec

Well-known member
Joined
Nov 18, 2015
Messages
2,878
Theres a possible candidate for mains transformer from a seller stateside, he has a few other output transformers for sale too . 

https://www.ebay.ie/itm/154130618682

 

Matador

Well-known member
Joined
Feb 25, 2011
Messages
2,047
Location
Bay Area, California
If you end up building that Spitfire, I suggest adding in a switchable NFB loop as well.  Networks in the feedback path are one of the coolest places to tinker with the overall response of the amp.
 

Potato Cakes

Well-known member
Joined
Jul 1, 2014
Messages
1,876
Location
Nashville, TN
Matador said:
If you end up building that Spitfire, I suggest adding in a switchable NFB loop as well.  Networks in the feedback path are one of the coolest places to tinker with the overall response of the amp.

I would probably need some suggestions to start messing with that. Right now I want to focus on it working well with close to as no noise as possible.

Thanks!

Paul
 

mhelin

Well-known member
Joined
Mar 12, 2005
Messages
532
Location
Tampere, Finland
Regarding the "cone cry", meaning the speaker drivers and the sounds, these days it's very common to use amp modelling with cabinet IR's (impulse responses and DSP convolution) for an example. Guess you know it already, anyway check the software and video on https://audioassault.mx/air.php Also the plugins on https://neuraldsp.com/plugins have a very good selection of cabinet models (and amp models second to none), another local guy (also supplying NDSP with some IR's) is ML Sound Lab and their MIKKO plugin named after me - not really :)  https://ml-sound-lab.com/products/mikko-free-install

Obviously you don't have to use software for amp modelling if you've already got a good amp (though the one you are building doesn't seem to be very hi-gain one). Just be sure to add a clean DI output after the output transformer, it can be just another line level step-down output transformer (not sure which ratio is good, 1:1 gives out 2.83 volts for one watt of power, generally output voltage is the square root of power*impedance). For the speaker driver I would recommend some very light paper cone driver, I've got a Vintage Series Weber 12F150 (not alnico though) driver (https://tedweber.com/) in my Tweed Deluxe clone which sounds just excellent. Speaker sound, the "cone cry", is the most important factor in amp sound, imho. SS amps can sound very good (just different sound) if they used proper drivers which they don't usually do. I haven't tried Trademark TM-10 but it's Behringer clone (GM110) has some Jensen derivated driver which sounds just perfect for the "analog modelling" (just an EQ) amp. 10 inches is good size, btw.
 

solkatten

Well-known member
Joined
Apr 3, 2021
Messages
112
Location
sweden
Hi you could very easily imitate the sonic virtues of tube rectifier by adding serial reisistance between the rectifier and the first filter cap. (ca. 150 Ohm power resistor) You could make it switchable.
 
Last edited:

Latest posts

Top