first amp build 6g3

[Telenut62]

http://www.hoffmanamps.com/

[charisjapan]

Originally Posted by burninwordz

the chassis dimensions are 18x6x2 1/2 THANKS
Attachment 130600

Attachment 130601

Man, that must have made a racket!! Great job on that chassis. I envy the space, the tools, and the FUN!!

[burninwordz]

Man, that must have made a racket!! Great job on that chassis. I envy the space, the tools, and the FUN!!
Hi charisjapan It's the old banging and shaping to get things done!!!thanks

[burninwordz]

Hi guys thanks for viewing my build, been busy working here's 'some pics of the 6g3 ,thats me trying to learn how to use my clausing mill machine, I put the trannies,tube sockets, two pots ,just to get the feeling of the build. thanks will be posting soon with more updates !!!!

[andyfromdenver]

It has a cool "distressed" look! Guitar makers charge big $ for that... I see a business model :)

[burninwordz]

HI guys i'm a bit confused here, on the 6g3 schematic the voltage going to the 6v6gt reads 365v but the filmosound tranny says 240 v does this mean that i'll have to change the pt for this build ,G-LOG used the filmo trannys for his build but with some mods will i have to do the same , HELP NEEDED !!!!!! thanks

[printer2]

Using a solid state bridge rectifier you will get 335Vdc (240V X 1.4 = 336V) minus losses in the circuit, maybe 320-325V. The Tweed Vibrolux and Harvard ran in this range, you are a little low to be 100% correct but not enough to worry about. You might put out 12W rather than 14W.

Hope you do not mind my asking, but I am a little confused. Are you using 6V6's or 6bq5's?

[Keyser Soze]

the two amps use different rectifiers. Even if the transformers were identical the rectified DC voltages might not be the same.

The big problem you have is that a 6g3 uses a 5 volt rectifier tube - a 5ar4 (aka GZ34.)

It is hard to tell from the pictures, but judging from the tube complement it looks like your power transformer does not have a 5 volt filament tap.

In which case you will have to deviate from the actual 6g3 schematic. You can stay with the 6ca4 rectifier, or maybe switch to solid state rectification. I'd try the tube rectifier first.

[G-log]

It looks like you have what Keyser says. It its an oddball model, for sure. I did notice that you do have 6Aq5 tubes in there. I didn't know there was a model using those tubes.Bell & Howell made so many different ones.There are a ton of schematics in this file to help you out .
http://www.film-tech.com/warehouse/manuals/AMPS.pdf

[printer2]

6AQ5's or 6BQ5's? Is it a 7-pin tube or a 9-pin, hard to tell by the pictures. A tube rectifier is doable but it would use up more precious volts. Would make sense with the transformer voltage and them being 6AQ5's. Then the question is what output tube do you want to run? Get new sockets or use what you have? May not end up 100% 6G3 but depends how close you want to get.

[burninwordz]

hi guys I'll start by answering PRINTER2 question:I wasn't sure if the original tubes work,when I plug the filmo some smoke started to come out of one the resistors next to the filters ,and the 6CA4 looks burned out.so I decided to use new ones ,avoiding future headaches, and the 6bq5''s are 9 pins I ordered new sockets for 6v6's and kept the 12ax7 sockets and build it as close to the 6g3, here's a pics of the 8399 model transformer schematic.



Do I need to build a bridge rectifier or am i good with to go ahead ?

[burninwordz]

Another question: Using a bridge rectifier does it change the sound ?or it does not affect it at all ,thanks guys for the help well appreciated ,another question:How can i tell if my transformer has a 5 volt filament tap ? remember all this tube building is new to me and i'm building it from scratch not having any instructions on how to build it and i'm following all your feedback,thanks, as allways comments welcomed!!!

[printer2]

No you do not need a bridge rectifier. When you gave the transformer voltage I thought you were measuring across the secondary terminals and not from one to the center tap. You can go with a tube rectifier or a couple of SS diodes if you want.

The schematic above shows a 110V tap on the primary, do you have one? If you hook up 120V to this your secondary voltage will be about 10% higher. The heater windings will also be 10% higher but you could put a couple of resistors on either side of the winding to knock it down.

Was the 240V you mentioned written on the transformer or did you measure it? If you could measure the voltage on the transformer with no load and then measure the resistance of the secondary we could throw the numbers in Duncan's PSU Designer (a power supply simulator) and tell you what you will get for different options.

[burninwordz]

THANKS PRINTER2 that's the exact schematic for my filmo model,I've been reading filmosound mods in different site's and not having no info about the amp,after reading a mod were that person 's concern was his tranny voltage was 240v's .I'm assuming that all of the filmo amps run on the same voltage so I was worried if it was o k to build it with that voltage level and after you guy's started feeding me with info I went looking to find out the voltage level in the schematic and was relieved to realize there won't be a problem for now with the voltage thank you guys push us noob's to learn and do our homework so we could get it right!!!!!

[telex76]

Cool project, good luck.

[burninwordz]

Thanks telex76, that's appreciated

[burninwordz]

Just got this in the mail ordered from AES,and I grab my chassis and started putting parts on it, (ouch something just fell in my eye) seriously guys allways wear protective sunglasses when drilling or cutting any type of material (it a bugger)so here are some more pics of the 6g3 with finally new parts!!!!! thanks as always comments welcomed.

[burninwordz]

Hi guys a tech question about capacitors. In the 6g3 schematic it reads .01UF@ 400v ,can i use a .01uf@630v, Does this in any way affect the amp thanks .????

[G-log]

Nope!

[milocj]

That "nope" means that it won't affect the amp. When you go higher in voltage than the specs its alright as it just adds a safety factor. You normally don't want to go lower in voltage value unless you know for sure that the cap used was only used due to ease of availability and not due to the voltages present (like in a guitar's tone control).