Monkeymatic Black Butte (univalve build)

General discussion area for tube amps.

Moderators: pompeiisneaks, Colossal

User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

Re: Monkeymatic univalve build

Post by xtian »

Applied gun stock oil, shielded inside with copper foil, applied orbital sander to bottom plate and attached to cabinet.

IMG_8794.jpg
IMG_8795.jpg
You do not have the required permissions to view the files attached to this post.
Last edited by xtian on Wed Dec 06, 2017 3:49 am, edited 1 time in total.
I build and repair tube amps. http://amps.monkeymatic.com
User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

Re: Monkeymatic univalve build

Post by xtian »

Progress pix.

IMG_8798.jpg
IMG_8800.jpg
You do not have the required permissions to view the files attached to this post.
I build and repair tube amps. http://amps.monkeymatic.com
User avatar
M Fowler
Posts: 14017
Joined: Wed Jan 16, 2008 2:19 am
Location: Walcott ND

Re: Monkeymatic univalve build

Post by M Fowler »

Really cool project that turned out looking good.
User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

Re: Monkeymatic univalve build

Post by xtian »

Having wired up the heaters, I have a question about the DC heaters for the preamp tubes.

I'm reading 8.4vDC between pins (4+5) and 9.

I have 6.7vAC heater tap. So, 6.7 x 1.4 (FWB, cap input) = 9.38, subtract one volt for the two diodes, gives 8.38vDC. Even when the heaters drop to 6.3v under load, the DC heaters will still be 7.82v.

Do I need a voltage regulator? Why didn't THD use one? How can this circuit work properly?

See here for schematic: http://ampgarage.com/forum/viewtopic.ph ... 60#p379458
I build and repair tube amps. http://amps.monkeymatic.com
User avatar
pompeiisneaks
Site Admin
Posts: 4222
Joined: Sat Jan 14, 2017 4:36 pm
Location: Washington State, USA
Contact:

Re: Monkeymatic univalve build

Post by pompeiisneaks »

xtian wrote: Tue Dec 05, 2017 1:46 am Having wired up the heaters, I have a question about the DC heaters for the preamp tubes.

I'm reading 8.4vDC between pins (4+5) and 9.

I have 6.7vAC heater tap. So, 6.7 x 1.4 (FWB, cap input) = 9.38, subtract one volt for the two diodes, gives 8.38vDC. Even when the heaters drop to 6.3v under load, the DC heaters will still be 7.82v.

Do I need a voltage regulator? Why didn't THD use one? How can this circuit work properly?

See here for schematic: http://ampgarage.com/forum/viewtopic.ph ... 60#p379458
My first guess would be that heaters have a max rating, depending on tubes, of 50 to 100V. I've looked up the typical 12A*7 types and they all seemed to be 50V, and power tubes I looked at (EL34) were 100. This is where they tend to burn up. Otherwise you're just generating more electron flow. It may still shorten the life of the tubes, but I don't think it will cause any kind of failure to operate (chooch as a known youtube canuck calls it).

~Phil
tUber Nerd!
User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

Re: Monkeymatic univalve build

Post by xtian »

pompeiisneaks wrote: Tue Dec 05, 2017 2:49 amMy first guess would be that heaters have a max rating, depending on tubes, of 50 to 100V. I've looked up the typical 12A*7 types and they all seemed to be 50V, and power tubes I looked at (EL34) were 100. This is where they tend to burn up. Otherwise you're just generating more electron flow. It may still shorten the life of the tubes, but I don't think it will cause any kind of failure to operate (chooch as a known youtube canuck calls it).
Heater voltage should be 12.6 for series, 6.3 for parallel. Most folks recommend doing something to lower the heater voltage if it's up in the 7.x range. What are you talking about?
I build and repair tube amps. http://amps.monkeymatic.com
User avatar
didit
Posts: 976
Joined: Thu Sep 25, 2008 3:37 pm
Location: Canada

Re: Monkeymatic univalve build

Post by didit »

xtian wrote: Tue Dec 05, 2017 1:46 am Do I need a voltage regulator? Why didn't THD use one? How can this circuit work properly?
Loaded or open unloaded? Reasoning behind the separated filament windings on the original schematic. Recommend reading up on transformer regulation. This varies across brand/models. Apparently somewhat expensive to achieve. THD would get a transformer that holds closer to spec for 2x300mA static load?

Speculated of course .. Ian
User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

Re: Monkeymatic univalve build

Post by xtian »

Yes, unloaded--good point. I loaded the tubes and tested, and I get 6.6v on the heaters. Not bad. Thanks, Ian!
I build and repair tube amps. http://amps.monkeymatic.com
User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

Re: Monkeymatic univalve build

Post by xtian »

Finished and play testing.

PTP is a PITA.

IMG_8821.JPG
IMG_8812.JPG
IMG_8821.JPG
IMG_8827.JPG
You do not have the required permissions to view the files attached to this post.
I build and repair tube amps. http://amps.monkeymatic.com
User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

Re: Monkeymatic univalve build

Post by xtian »

Final layout.

Monkeymatic Univalve layout.png
You do not have the required permissions to view the files attached to this post.
I build and repair tube amps. http://amps.monkeymatic.com
User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

Re: Monkeymatic univalve build

Post by xtian »

I am having trouble with ringing and oscillation. I've done quite a bit to try to isolate the issue.

When power tube is pulled, just V1 and V2 installed (both preamp tubes are required to see the issue). As I turn up Volume, I can see the "ring" (photo attached), and this "ring" reaches 100v p-p at the output of V2b.

ring.jpg

(When the power tube IS installed and I turn up the volume, it breaks into oscillation at about 10KHz.)

I have tried adding a 22K grid stopper to V1b, tried 250p across anode and cathode of V1b. I have tried several different preamp tube swaps.

But, with V2 pulled, V1 does not show any signs of ringing or oscillating, so I guess I need to focus next on V2.

Notice that V1b and V2a are DC coupled. Can I add a grid stopper to V2a?

Any other tricks?
You do not have the required permissions to view the files attached to this post.
I build and repair tube amps. http://amps.monkeymatic.com
User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

Re: Monkeymatic univalve build

Post by xtian »

I added a 22K grid stopper to V2a. No change.
I build and repair tube amps. http://amps.monkeymatic.com
User avatar
dorrisant
Posts: 2613
Joined: Tue Sep 21, 2010 1:27 pm
Location: Somewhere between a river and a cornfield
Contact:

Re: Monkeymatic univalve build

Post by dorrisant »

Very nice!! Expect clones... at least one from here. Sorry you are having issues... subscribed.
"Education is what you're left with after you have forgotten what you have learned" - Enzo
tictac
Posts: 610
Joined: Fri Mar 31, 2006 4:42 am

Re: Monkeymatic univalve build

Post by tictac »

Your grounding looks "daisy chained" to me; could the way you're using the volume control lug as a star ground point be an issue?

Maybe try adding a grounded copper buss wire, separate the grounds and attach them to the buss....

Just a thought...

TT
User avatar
Colossal
Posts: 5038
Joined: Sat Oct 20, 2007 9:04 pm
Location: Moving through Kashmir

Re: Monkeymatic univalve build

Post by Colossal »

Xtian,

Are you running that NFB/presence control on the fake PI? Maybe disconnect the feedback temporarily...
Post Reply