Author Topic: 6G9 Build (Read 7555 times)

TIMBO · « **on:** January 31, 2015, 06:01:46 pm »

Hi guys, Taking a break form the challenges of old amps

After seeing Plexi50 thread on the 6G9 Blonde http://el34world.com/Forum/index.php?topic=17334.msg173562#msg173562 and having a full 18w set in the cupboard, this was a great looking build.

In the throws of getting some parts required, a couple of things popped up................
The PT http://www.classictone.net/40-18035.pdf gives me some options on the circuit.
The 120mA rating is enough for 2x EL84 and 5x 12AX7.
An EZ 81 has plenty mAs to do the job.
Q. Is there any good/bad reason to stick with the EZ81 or going to an 8pin type rect?
Trying to stick to the original schematic, it does not have screen resistors on the power tubes and comparing to Dougs stout, 1k resistors used. (a no brainer so they will be added)
There is also no grid resistors on the power tubes and 8.2k seems to be the norm?
There is no coupling cap at the entrance to the PI, again needed?

sluckey · « **Reply #1 on:** January 31, 2015, 07:50:24 pm »

Quote

Is there any good/bad reason to stick with the EZ81 or going to an 8pin type rect?

EZ81 is fine for a pair of EL84s.

Quote

There is also no grid resistors on the power tubes and 8.2k seems to be the norm?

I'd use them.

Quote

There is no coupling cap at the entrance to the PI, again needed?

Not needed. Each preamp already has a coupling cap prior to the mixing resistors.

TIMBO · « **Reply #2 on:** January 31, 2015, 09:45:44 pm »

Thanks Sluckey.

TIMBO · « **Reply #3 on:** February 02, 2015, 12:32:22 am »

Hi guys, Another question, can I use one of the MIXING resistors (220k) as my insertion point for the reverb. Thanks

sluckey · « **Reply #4 on:** February 02, 2015, 08:57:14 am »

Quote

can I use one of the MIXING resistors (220k) as my insertion point for the reverb.

Probably. But now you will need a coupling cap at the input of the PI.

TIMBO · « **Reply #5 on:** February 13, 2015, 03:46:15 pm »

Thanks Sluckey, A slow start. I've had to do a lot of

with the layout.

TIMBO · « **Reply #6 on:** February 15, 2015, 02:06:38 am »

Hi guys, The next bit is a bit OLD school, an idea that I don't think is new but used by our local amp builders back when.
http://www.ozvalveamps.org/goldentone/suitcaseunder0526rdw.jpg
The "Valve Tree" was used by a couple of sockets and using the pins was away of mounting components directly to the sockets.
Using a disc of PCB is less bulkie and simple to use and great for tight places.
Another idea is to use bottom mounting sockets, this makes "PREFABING" outside the chassis a easier task and the finished unit can be easily mounted.
The layout sheet shows the component position.

Ed_Chambley · « **Reply #7 on:** February 15, 2015, 09:55:10 am »

Timbo, I have never seen this "Valve Tree" PCB. Did you make them? If not, where did you get them?

sluckey · « **Reply #8 on:** February 15, 2015, 10:15:56 am »

Quote from: Ed_Chambley on February 15, 2015, 09:55:10 am

Timbo, I have never seen this "Valve Tree" PCB. Did you make them? If not, where did you get them?

They are also called vector sockets. They were popular in compact communications radios. Angela and eBay have this style...

TIMBO · « **Reply #9 on:** February 15, 2015, 01:12:59 pm »

Thanks guys, Ed, I had to make them just to see if it would work.
It's a costly thing to get made, the design part was going to be about $250

Willabe · « **Reply #10 on:** February 15, 2015, 06:09:21 pm »

TIMBO · « **Reply #11 on:** February 15, 2015, 10:36:47 pm »

Willabe · « **Reply #12 on:** February 15, 2015, 11:05:30 pm »

TIMBO · « **Reply #13 on:** February 15, 2015, 11:45:49 pm »

Willabe · « **Reply #14 on:** February 15, 2015, 11:54:29 pm »

TIMBO · « **Reply #15 on:** February 16, 2015, 12:05:11 am »

drew · « **Reply #16 on:** February 16, 2015, 01:36:00 am »

Interesting approach. Sort of a 3D/stand-up version of Merlin's development boards?

TIMBO · « **Reply #17 on:** February 22, 2015, 02:56:41 am »

Thanks guys, A bit of progress..................

kagliostro · « **Reply #18 on:** February 22, 2015, 03:20:49 am »

Very Cool Job TIMBO

when you finish that amp (that I consider a wonderfull job), perhaps this will be the next frontier ?

Franco

TIMBO · « **Reply #19 on:** March 10, 2015, 01:02:36 am »

Hi guys, Last thing to tidy up.
The fender schem has a 27k feedback resistor that is connected to the 8ohm speaker tap.
For convenience it would be easier to connect the feedback resistor to the unused 16ohm tap, so can the same FB resistor be used or does it have to be halved or doubled. Thanks

kagliostro · « **Reply #20 on:** March 10, 2015, 04:04:20 am »

Ciao TIMBO

http://el34world.com/Forum/index.php?topic=18132.msg184302#msg184302

Read Sluckey & DummyLoad

Franco

TIMBO · « **Reply #21 on:** March 15, 2015, 03:17:09 am »

Thanks K, I connected the 27k to the 16ohm tap.
This one fired up well.

I was unable to crank it up, but at low level every thing was working.
The voltages are close the fender schem, although I thought the EL84 plates would be a bit lower as these are 18w transformers.

TIMBO · « **Reply #22 on:** March 15, 2015, 03:21:52 am »

O yeah, there was some concern on hum due the proximity of the components, this one is very quiet.
Updated Schematic with voltages.

trobbins · « **Reply #23 on:** March 15, 2015, 06:42:23 am »

Hey Tim, is the centre bolt connected to the local gnd for the valve - as per grounding the central spigot in a valve base? Grounding the spigot in nine-pin novals was certainly a key improvement (and necessity) compared to octal bases. Ciao, Tim

sluckey · « **Reply #24 on:** March 15, 2015, 07:55:34 am »

I like your socket trees. They remind me of some old military gear.

TIMBO · « **Reply #25 on:** March 16, 2015, 01:02:17 am »

Hey Tim, I did not ground the bolt, only because I had to etch the boards myself and I just used a marking pen to do the traces, so it was a bit tight to do a trace around the bolt hole. The longest 3mm bolt I can get is 50mm long and at this length they only just fit the depth of the chassis.
I haven't come up with an idea to do a better grounding for each tube, I had thought of a third disc that would have all the grounds of the tubes connected on it, then a solid buss bar between tubes.

This would mean I would probably need a 75mm bolt, although I can get a 3mm threaded rod and cut it up.

trobbins · « **Reply #26 on:** March 16, 2015, 01:31:50 am »

Top credit for having a go at the tree hanger - I reckon they are great - if only I had some

The only hanger I've had a chance to use is the 5 eyelet strip that Hammond used to run 5 busbar wires along their organ oscillators tubes - they solder on to the central spigot - a bit cramped, but easy. I like to use the spigot wherever possible, as it makes a great low-noise ground point.

Maybe you'll inspire some Chinese clone company to make them - but that would mean you'd have to sell your versions for $50

kagliostro · « **Reply #27 on:** March 16, 2015, 03:35:28 am »

TIMBO, to me your job is great and you've been a really good craftsman

now you have finish and I don't think my idea for a ground connection of the bolt can be applied

the idea is to use nuts and a lug whasher (I hope is the correct name in english)

to have a ground connection between the two PCB or on the Top

Franco

TIMBO · « **Reply #28 on:** March 18, 2015, 03:46:05 am »

Thanks Guys, I think this one has turned out great, so I will investigate some more ideas with the next build I use this method on.

Post a clip ASAP. Thanks

TIMBO · « **Reply #29 on:** June 20, 2015, 01:50:04 am »

Hi guys, This one is just about done, needs a few touch up and where good to go.

TIMBO · « **Reply #30 on:** June 21, 2015, 02:27:45 am »

Hi guys, I was able to crank it up today and its GRRRRRRRRRRRRRR8.

Lots of good marshally grind but I think it could do with a touch MORE.
I like the crunch Doug gets with the STOUT TMB, so a close look to compare the circuit design.

The only real difference is around the PI and of course the power tube bias.
Is tweaking the PI going change the DRIVE any. Thanks

uki · « **Reply #31 on:** June 21, 2015, 06:46:13 am »

It is beautiful and very interesting, thank you for sharing !

VMS · « **Reply #32 on:** June 21, 2015, 02:48:57 pm »

Quote from: TIMBO on June 21, 2015, 02:27:45 am

Lots of good marshally grind but I think it could do with a touch MORE.

It seems that this is my mantra of the week, but have you tweaked the feedback resistor or tried the amp without the nfb like 18watt marshalls?

vicentebd · « **Reply #33 on:** June 21, 2015, 06:41:43 pm »

TIMBO biutiful amp and clean job

robrob · « **Reply #34 on:** June 22, 2015, 07:34:41 am »

Quote from: TIMBO on March 10, 2015, 01:02:36 am

The fender schem has a 27k feedback resistor that is connected to the 8ohm speaker tap.
For convenience it would be easier to connect the feedback resistor to the unused 16ohm tap, so can the same FB resistor be used or does it have to be halved or doubled. Thanks

Just to give an answer for future reference the 27k feedback resistor would need to be increased by multiplying by 1.414 (square root of 2) to yield the same level of feedback. 27k x 1.414 = 38.2k and 39k is the nearest standard resistor value. If you were moving from 4 ohm to 16 ohm you would multiply the resistor value by 2 (square root of 4) and going from 2 to 16 ohm you would multiply by 2.83 (square root of 8).

Welcome To the Hoffman Amplifiers Forum September 07, 2025, 08:41:09 am

Welcome, Guest. Please login or register. -User Name -Password
Home Help Search Login Register
Hoffman Amplifiers Tube Amplifier Forum » Amp Stuff » Tube Amp Building - Tweaks - Repairs » 6G9 Build

Choose a link from the Hoffman Amplifiers parts catalog
Mobile Device Catalog Link	Yard Sale Discontinued	Misc. Hardware
What's New	Board Building Parts	Amp trim Handles
Lamps Diodes	Hoffman Turret Boards	Channel Switching
Resistors	Fender Eyelet Boards	Screws/Nuts Washers
Jacks/Plugs Connectors	Misc Eyelet Boards	Tools
Capacitors	Custom Boards	Tubes Valves
Pots Knobs	Fuses/Cords	Chassis
Tube Sockets	Switches	Wire Cable

Welcome To the Hoffman Amplifiers Forum

Author Topic: 6G9 Build (Read 7555 times)