Brown Note Blue Monkey and Little Dummy Question

[Jjjp]

Can anyone help me out with biasing this amp- tubes seem to be paired. Is there a way to bias each tube individually? Have a matched quad but one tube is around 29mv and the other at 32mv. The other 2 match perfectly and are set at around 32-33mv. Also internal pots I know where the HRM eq pots are. Any ideas on the others- I'm trying to post picture of mine. I've attached a PDF with pictures. Lastly are there any tips on how to set the dumbleator buffer up (Brown Note version is called the Little Dummy)? Thanks very much.

[Structo]

Hey, welcome to the Amp Garage.

I'll try to help you.

Have you tried moving the power tubes around in different sockets to see if anything changes.

Like does the lower current tube follow that tube or stay at the socket it was in?

Personally I would not sweat a 3ma difference.
It can actually make the power amp sound a bit sweeter if there is a bit of imbalance.

Your amp has dual bias controls. You can adjust each side of the push/ pull output.

As far as the trimmer pots go.
I have labeled the trimmers that I am sure about but the one at the top left, I'm not sure on.
I don't know if that is a hum balance type bias adjustment or what.
Have you had your meter connected at the bias test points while adjusting that trimmer? (be sure to take a picture or mark the trimmer so you know where you started).

Most Dumble style amps sound there best biased on the cold side.
Depending on what your power tube plate voltage.
Usually around 60% sounds good, plus your tubes will last longer.

As for the Dumbleator, usually time based effects like delay or reverb work well there.

What most of us that have D'lators do is set the Send about unity (around noon).
Then set the return to were it is not overdriving the loop.

If you set your pre gain volume on the amp around noon to 1:00 and the master about the same, that gets into the sweet spot on the amp.
Then control the actual volume (loudness) of the amp with the Output pot on the D'lator.

That is assuming your loop has three controls, Send, Return and Output.

Hope this helps.

[Jjjp]

Here is a partial gut shot. Front of amp is towards the bottom of the photo. 3 small pots in the middle are the HRM EQ pots. It's the other 4 I'm wondering about- 3 vertically mounted and a smaller one horizontally mounted. Thanks for any help identifying and advising on adjustment of these.



[IMG768]http://i1217.photobucket.com/albums/dd3 ... amp006.jpg[/img][/img]

[Jjjp]

Thanks so much Structo- I will take a look at all of this and see where it leads me. The Little Dummy has from left to right the following controls:
Send pot, bright switch,recover pot, return pot, bright switch. It seems like these would correspond as send is send, recover is return, and return is output if I'm understanding things correctly. Also it sounds like I should be biasing closer to 28mv rather than 35mv which is the high end of the recommended range. Are there any recommendations on the PI or NFA adjustments?

[ToneMerc]

Small pot at 6 o'clock is a high cut control that is triggered from the rightmost relay in the PAB mode only.

TM

[Jjjp]

Thanks ToneMerc. Are these pots normally tuned by ear or value? Obviously I'm new to Dumble style amps so I'm trying to find my way with this stuff. If possible I want to be able to tune the amp myself instead of bringing it to a tech.

[stelligan]

Look for guidance here: https://tubeamparchive.com/viewtopic.php?t=12875

Much good info on recommended settings for those trimmers and OD entrance trimmer in the first few posts. Happy trimmer trimming....

[Structo]

What is your plate voltage on the power tubes?

Here is the bias formula in case you don't have it.

(W * % / V = I

W = wattage of power tube (6L6GC is a 30 watt tube)

% = what percentage of 100% you want the bias at.
( most guys set their bias below 70%, I like around 60-65%)

V = power tube plate voltage (pin 3)

I = bias current in milliamps or ma

This is per tube, if you have two bias pots then each side will be a factor of 2x for the result of your math.

Example: you come up with 35ma. For each side that number will be
70ma.

[ToneMerc]

Thanks ToneMerc. Are these pots normally tuned by ear or value? Obviously I'm new to Dumble style amps so I'm trying to find my way with this stuff. If possible I want to be able to tune the amp myself instead of bringing it to a tech.

Adj Neg FB and hi cut are mainly season to taste. The OD tone stack trimmer settings will make or break an HRM and can require a fair amount of time spent to get the amp to your liking as well. FWIW, my first 100w D style amp was a BN BM reverb.
TM

[Jjjp]

Thanks for all the replies, I really appreciate the help. With respect to the biasing of the amp I'm used to biasing each tube on other amps I've had and don't quite get what the procedure is for paired tubes- if I adjust the bias it affects both tubes so should I average it out between the 2 tubes based on the values I want? I've been advised that a dumble likes a bias on the colder side of the value range. The range for my tubes is supposed to be 28-35mv. I'm setting the bias on one pair at around 29 and they're consistent. On the other pair, depending on the which tube I bias to 29, the other is either 24-25 or 33-34.