Have you checked the four 10W emitter resistors?

The Peavey Transtube does have the raising distortion characteristic, but THD only reaches about 3% before clipping. At low levels I didn't see the 2nd harmonic dominance, 3rd was always present at nearly the same level. It does sound kind of tube like, but not as warm as a real tube or my Bender preamp.

Link to Bender preamp: http://www.ssguitar.com/index.php?topic=3732.0

The Sunn Concert series is a very primitive early 70's design. There is no current limit other than the beta of the output transistors and the drive available through the drive transformer. The driver transformer has a primary and four secondaries. On some versions there is a trim pot in the driver stage, but no info anywhere I can find on how to tweek it. Probably a clipping symmetry adjustment.

There are two basic versions. The earliest is a "Flying Bridge" with a floating power supply of about 35V. Check that the four transistors and all the resistors are good. There should be very little DC on the output with no speaker connected, perhaps a Volt or two. If there is too much DC, a transistor is blown or a resistor has drifted or smoked. It is not uncommon for a short to develop in the driver transformer between the primary and one of the secondaries. This puts big DC on the output.

The second version is a conventional totem pole configuration with +/- 34V rails, but it still has the same driver transformer. This version has a 5 wire power transformer, the earlier version has an 8 wire power transformer.

If everything seems OK, a low beta output transistor is suspected. If you don't have a way to measure beta at high current, you'll need to replace all of them.

I'm not sure any 240V export versions of the Concert series were ever made, but some 120V ones were made in Mexico.

Edit: Schematic you posted is the early version.

Edit2: Note that the wire common to R305 and R307 connects to ground at point 33 on the PCB.

I like the simplicity of this design. It might make a nice beginner project. If not the whole amp, at least the power amp. It could run from a 24VAC wall wart with a couple of simple changes.

What are the transistor numbers?

The one thing rarely mentioned is that most of these supplies will operate from 100 to 250 VAC 50/60Hz input. You just need the right Mains cord or an adapter. I found a 48V 2A but haven't tried it yet.

Quote from: Charliegriffin on August 12, 2016, 04:56:57 AMAlso I forgot to mention the schematic calls for 2n5484 transistors but all I had on hand were 4401s that could be  my whole problem.

Do you mean 2N4401 ? That's an NPN bipolar transistor. The 2N5484 is an N-channel JFET.

MEF went down last night and was still down this morning. It's back up now.

Tone stack looks a little odd for a Marshall. Try C13:470pF, R24:33K, C14:.022uF, C15:.022uF.

With 25V rails I would expect an 8 Ohm total load for 30W. Speakers should be 2X 16 Ohm.

Bad software doesn't kill power supplys. Not even Microsoft.

It's working now. Seems a little slow to respond but that could be the new Firefox 47.0.1

Edit: This site seems to be working fine, maybe a little better than before!

I'm still getting a timeout. I even re-booted and thought it was working but it was just the last valid page from two days ago.

Three parallel "branches" of 8 Ohms results in a load of 2.66 Ohms. So connect three pairs of 4 Ohm speakers in series, then connect those series pairs in parallel.

Is the Silvertone 1485 head the one with four 6L6s and two output transformers? That won't work well with this cabinet because you need two loads of 4 or 2.66 Ohms each.

In a series circuit, the resistor with the highest resistance will have the most dissipation. Calculate the current that will result in that resistor being at it's maximum, then check that the other resistors will be at or below their rating at that current.

In a parallel circuit, the resistor with the lowest resistance will dissipate the most power. Calculate the Voltage that will result in that resistor being at it's maximum, then check that the other resistors will be at or below their rating at that Voltage.

As a practical matter, running resistors at their maximum power rating is not a good idea. If they are on a PCB, it will usually make the board turn black. The resistor or it's solder joints will fail. A resistor's power rating is based on temperature. If they are in a warm environment, they must be de-rated. You can run resistors beyond their power rating for short amounts of time as long as the resistor does not get too hot. To be conservative, don't run resistors more than about half their power rating.

Quote from: exztinct01 on June 16, 2016, 05:52:38 PM
how about that tda8932 amp in a thread in diystompboxes http://www.diystompboxes.com/smfforum/index.php?topic=114335.0?

Class D amps can sound pretty bad when they clip like they do frequently in guitar amps. What the OP said in the diystompbox thread is not too encouraging but it won't cost much to buy one and experiment.

The 3904/3906 transistors are not intended to handle very much power, only about 0.35Watt. They are just marginal in the 9V battery circuit. They will work OK in a preamp though. You really need some real power transistors, ones that will bolt up to some kind of heat sink.

The first thing you need is a power transformer. Probably the easiest thing to find is a 24VAC "wall wart", one rated at 40VA is about as big as you can find. This will work well to make a power amp good for about 12 Watts at 8 Ohms. The 24VAC transformer will make about 33VDC after rectification and filtering.

The circuit in this thread: http://www.ssguitar.com/index.php?topic=3747.0 will work OK on 33V. The transistors in the original article will be impossible to find and the layout will need to be modified for most current production power transistors. You can use the 2N3904 for Q1 and Q3 and a 2N3906 for Q2.

See if you can find MJE3055T for Q5 and MJE2955T for Q4.