I've gotten some feedback on this amp from Tube Asylum
Hi Josh - Re amp
project, Sean wants to swap the output tubes in his (my old) amp back to EL 34s
(the way I had it) from its current 6l6. Found a couple of places on the web
with appropriate documentation and it looks like a pretty simple deal. Think we
can knock it off in an afternoon as we dont have to switch sockets. Also might
want to take a look at the input section as the schematic shows it has swapped
in lower powered less bright tubes (cant remember the # maybe the 12AT7 ) for
the standard 12AX7 and I dont remember what I tubed it with, or for that matter,
what Sean has put in it over the years. Also should give the pots a cleaning and
replace the knobs, about half of which are broken.
I think this is the kit for it: http://www.torresengineering.com/elconkit.html
Here's a nice Tube FAQ that has a detailed section on transformers as well as other good tube info:
Designing and hand winding transformers is not terribly difficult, but it does require information and skills that are relatively hard to find. You are unlikely to save a whole lot of money unless used or broken parts are cheaply available to you. You may want to do this if you feel that you were selected by some deity to take this on as a life work. First, take a transformer apart. A burned out tube-type power transformer will do. Do this carefully and slowly, imagining how you would have put it together in the first place to get it the way it was. This is an excellent introduction to the manual skills and materials needed to successfully produce one on your own.
Also, I recently took shipment on this wild amp I found on ebay. It's much bigger and heavier than it looked in the picture, and has cleaned-up gorgeously. I'm afraid to power it up as the underside is quite corroded. Gotta fix that digital camrea so I can post pics...
Matching speakers to amplifiers
Matching Microphone to Input
Impedance: matching your speakers to your amplifier
12DW7 - dual triode, half a 12AX7, half a 12AU7
12AU7 - dual triode, mu=20
12AT7 - dual triode, mu=60
6CG7, 12BH7 - dual triode, good driver tubes
6GU7 - like 6CG7, but better
6GK6 - great output tube, same as 6BQ5 with different pin-out
6AF4, 6ES5, 6ER5, 6HQ5 - triodes
6BY5 - nice rectifier tube with isolated 6V filament
You could use two 6GK6s plus the 12AT7 (or a pair of 6AF4s) to make a nice little single-ended amp
- Tom Bavis
I find general purpose irradiated vinyl insulated,600V,105 deg C rated hookup wire from brands like Alpha, Carol Belden etc. to be fine performers. You have a wide range of gauges in both solid and stranded (all these brands are tinned Cu) and most colors. The ir vinyl stands up to the rigors of normal soldering w/o melting and looking bad. I tend to use 20 or 22 ga solid for low current apps and 18 for higher current apps like heaters. The 16ga is a little unwieldy even in stranded form so I don't use it much. Digikey carries Alpha and General Cable brands although only in 100ft spools. Actually, 100ft isn't as much as you might think.
Some like teflon insulated wire but I feel that it's overkill for most apps. It's also expensive and gauge and color selection is more limited. Digikey also carries the Alpha brand of this but with the 100ft minimum. Many DYI suppliers also carry tfe wire in much smaller minimums. - Steve Oda
Why? Pure, unadulterated-by-logic lust! it's a single channel tube eq that uses 12ax7 tubes.
The first commercially available (for the consumer market anyway) tube equalizer in the mid 50's. It was called the Blonder Tongue "Audio Baton", used 12AX7 tubes throughout and had 9 frequency bands. (they had a pretty nifty way of graphically representing the relative amount of gain/cut... I can give more detail if anyone gives a hoot) The designer's name is Ben Tongue (see his website below). He also holds the patent. The schematic is here: http://www.triodeel.com/images/b9b.gif
There was a model B9 and a B9B. The major difference being that the B9B had a slightly increased B+ voltage and the upper frequency band characteristics were changed a bit. - Gandalfcrow (AA)
This guy replaced all the caps and made his work perfect: http://www.endino.com/photo9.html
It was designed by this guy named Ben H. Tongue
Here's an interview with Mr. Tongue
C1 (.1uf/16v ceramic) cap does horrid things sonically, replace it with most any poly cap for a big improvement.
A small muffin fan (I like a 220v fan on 110v - runs sloooow) exausting up on top of the case will keep the temp way down.
As you've guessed, the bias is not adjustable - the ST35 uses cathode/self bias. I've tried individual bias resistors in an ST35. Although it sounds like a good idea, it sounded really poor IMHO. I'd stick with the original design. The EI 6BQ5's sound pretty darn nice and are quite inexpensive.
- Gary Kaufman
The Dynaco ST-35 is "Cathode Self Biased" and has a common 90 Ohm resistor attached to all 4 power tube cathodes to Ground that determines the current flow through the power tubes at idle. There is no adjustment. This requires use of a fairly well matched quad of power tubes.
This 90 Ohm resistor causes the power tubes to idle a little "hot" in my view, so in my ST-35 I changed this resistor value to a 120 Ohm (about 15 Watt) resistor.
Also, the tall silver Multi Cap can has 4 Capacitors in it. They are 3 filter caps for the power supply that may or may not need replacing. The forth Capacitor in the Can is the Cathode Bypass Cap, and I would replace it with a better quality cap, but one that would fit in the very small space (barely 1/2 inch) available on the underside of the top chassis
Also, you might wish to upgrade the coupling caps on the two PCB's with a bit better quality. I found that Solens fit the PCB space available nicely.
With just a few upgraded capacitors, and a new set of NOS tubes, the ST-35 will perform at a very high level, as it is one of the very best Push Pull designs ever.
Get a stable 10amp Variac. After soldering in your new cap AND double
and triple check your connections and polarity!
Replace any indirect rectifier (like a 5AR4/GZ34) with a direct
rectifier (like a 5Y3GT). Plug all tubes in & have speakers connected.
Volume at zero. No inputs.
Start at 60 volts VAC, for one-two hours. Check for anything unusual
(smoke, smells, etc). If all okay after 2 hours, ramp the Variac up to
80 volts (another 1-2 hours). Continue this trend until you reach 118
I find slowly ramped-up or formed electrolytic caps last a lot longer
than ones which aren't.
Strategies to Repair or Replace Old Electrolytics
A 13.5 x 99.0 cm - 16mm
B 13.5 x 33.4 cm - 13mm
C 13.5 x 59.5 cm - 13mm
D 13.5 x 13.4 cm - 13mm
E 13.5 x 41.0 cm - 13mm
F 13.5 x 29.2 cm - 13mm
G 13.5 x 43.3 cm - 13mm
H 13.5 x 44.0 cm - 13mm
I 13.5 x 33.4 cm - 13mm
J 13.5 x 40.0 cm - 13mm
K 13.5 x 25.0 cm - 13mm
L, M 35.0 x 99 cm - 13mm
Converted to inches (cm / 2.54, then decimals * 16, rounded up to the nearest 16th):
A 5 5/16" x 38 15/16" x 5/8"
B 5 5/16" x 13 1/8" x 1/2"
C 5 5/16" x 23 7/16" x 1/2"
D 5 5/16" x 5 1/4" x 1/2"
E 5 5/16" x 16 1/8" x 1/2"
F 5 5/16" x 11 1/2" x 1/2"
G 5 5/16" x 17 1/16" x 1/2"
H 5 5/16" x 17 5/16" x 1/2"
I 5 5/16" x 13 1/8" x 1/2"
J 5 5/16" x 15 3/4" x 1/2"
K 5 5/16" x 9 13/16" x 1/2"
L, M 13 3/4" x 39" x 1/2"
Home Depot, here I come!
Arglo Electric supply
Gettens Electric Supply
Allite Electric Supply
CED Lowell Electrical supply
Wellesley Electrical supply
Design Lighting & Elec. Supply
Maine electrical Supply
All electric Supply
Roberts Electrical Supply
Cape Electric Supply
LJ Macken Electronics
...includes links to pages about putting new capacitors into the old can.
Choosing Values of Large Electrolytic Capacitors
For electrolytic capacitors, the same rules apply, except that you can safely use a capacitance value that is considerably higher. In general, you can go as much as 100% higher than the original capacitance value.
For example, when replacing a 10-mfd electrolytic capacitor in the radio's power supply, it is OK to use a 20-mfd or 22-mfd replacement. Likewise, you could replace a 20 with a 33. The higher capacitance may do a slightly better job of removing 60-cycle AC line "hum" from the audio output of the radio. It is not unsafe to go even higher, but you generally won't notice any improvement and the higher-value capacitors (33 mfd, 47 mfd, and so on) are significantly more expensive. Don't waste money on a 100-mfd electrolytic if your radio sounds great with a 20-mfd unit!
Substituting for Unavailable Values
In a pinch, you can combine two capacitors to create one with the desired value. The rule to remember is that when two capacitors are wired in parallel, their values are added.
For example, say that you need a .04-mfd capacitor, but all you have on hand are .02-mfd units. Wire two .02s in parallel, and�voila!�you now have a .04-mfd capacitor. Likewise, wiring two 10-mfd capacitors in parallel creates a single capacitor of 20 mfd. Observe polarity when combining electrolytics (wire both positive ends together and both negative ends together). Both capacitors should have a voltage rating equal or higher than the original.
Is There An Audible Difference?
Russell O. Hamm
"The finest in handwound transformers and custom tube audio amplifiers"
Bottom line? I don't need one.
So I've ordered a set of these boards from Jim Sullivan:
Replacement circuit boards for Dynaco ST-35
I've ordered these 2 kits:
(click image for details)
(click image for details)
They seem to be very straightforward beginner-type projects and the result will be cool stomp boxes that I can use and show off to my friends.
Re: ST-35 - blowing fuses - help!
I would bet the Quad cap is going bad and a previous owner bypassed the first
bad section and no another is going south. Just order a new 4 section can from
www.tubesandmore.com and rewire it per the schematic. They have 2 that should
fit the bill a original with twist locks and a JJ telsa that clamp mounts which
is about a third the cost but doesn;t look factory original.
Walter G. Jung and Richard Marsh
Stock up on the following: resistors (good mix of 1/4W, 1/2W and 2W types as well as some 5W/10W cement power resistors), capacitors (different values and atleast 350V ratings), switches, grommets, input/output jacks, wire (different gauges and colors), knobs, hardware (machine screws, toothed washers and bolts) and terminal strips. Try to land power transformers, empty chassis, common tubes (6SN7, 12AX7/12AU7, 5AR4, etc), random output transformers, etc. as well. Remember - think like a pack-rat, act like a pack-rat.... be a pack-rat.
I'm looking for a replacement quad capacitor for my Dynaco ST-35.
It was Dynaco part # 297227, 3" tall, 1.375" dia
60mfd /450 V
40mfd /450 V
20mfd /450 V
100mfd /25 V
(Response from Audio Asylum posting)
Yep that is the 60mF section that is left unconnected which was the first
section after the diodes. If you look at the side of your cap it will show the
values and the symbol callout that correspond to the terminals on the bottom.
It was probably bad (the voltage is highest closest to the diodes) and left
unconnect just to get the amp working at some point in it's life. The voltage
would probably be close even with this section unconnected since your power
supply resistors still appear to be in the circuit. however the AC ripple would
not be totally filtered out of the B+ voltage going to the circuit, and the
noise and hum to the rest of the circuit will be higher.
The quad cap you found could work but it will fall short of what was originally
in the amp. The original quad cap in that amp is a four section. The first
three sections being 60mF, 40mF, and 20mF all at 450Vdc for the high voltage
filtering. The last 100mf at 25Vdc is for the bias supply.
You can check out Antique electronics supply I think they have some quad caps
that will take care of the high voltage but you will have to install a modern
100-220 mF 25Vdc minimum for the bias under the chassis (new caps of this value
are small and should fit no problem). Also this quad cap is taller than the
stock one and the cage will not fit with it installed.
Or you can use a JJ or LCR 50/50mF at 500vdc clamp mount for the first two
sections (you'll have to drill holes to mount the clamp however) and hide a
20-47mf at 450vdc under the chassis for the third cap (I don't know of one but
there may be one by Panasonic or Xicon or someone else that will fit). And
you'll still have to use a modern small cap for the bias here as well. Check
out Mouser or DigiKey for the modern type stuff.
I have not found a totally stock type solution for this amp and If you find one
please post it. My Stereo 35 has the original quad cap still in it and I know
one day I will have to replace it.
He sells replacement output boards and a filter capacitor board that replaces the stock 4-way filter capacitor (quad)
Understanding Electricity and Electronics by G. Randy Slone
A Beginner's Guide to Making Electronic Gadgets by R.H. Warring
Troubleshooting and Repairing Audio Equipment by Homer L. Davidson
How to Read Schematics by Donald E. Herrington
Converting to Cathode Bias
Learn Electronics - downloads
0nline electronics tutorial
- tube amp designs and detailed plans from an all-around wicked smart guy -
A recommended list of Hickok tube testers, and Ebay buying tips.
The Kappellmeister loudspeaker
"The Ultimate Demonstration Disc" Catalog No. UD095 Price: $15.98
An amp design that uses a multitude of power tubes connected in parallel to generate enough output current to drive loudspeakers without output transformers.
- John E. Karlson
ML = Mass Loaded
TQWT = Tapered Quarter Wavelength Tube
TQWP = TQW Pipe?
TL = Transmission Line
FTL = Focal Transmission Line (or Faster Than Light)
TS = Thiele/Small (parameters)
SPL = Sound Pressure Level