Sound City 120 is in a bad way

[Williamblake]

Hi! So a friend of mine has this Sound City 120 he would like to amplify his bass guitar with for gigging but it needs some repair and any thoughts to find out what's wrong with it are gladly appreciated.
When I got it it put out very loud hum and the tone control where crackling (6 EL34s no master volume crackling) and it put out a very low instrument signal. So i chopsticked the tubes and changed two but the  amp is still microphonic like a reverb tank and the hum and crackling didn't change.
But after i cleaned all the sockets the 18 Ohm resistor in series with the center tap was emitting smoke and at that point I thought i would ask for help before switching it on again.
I did measure some voltages, HT was at 500 something and behind V1's coupling capacitors was no DC but before the smoke rose there was 33 Volts at pin 2 V4, looking at the schematic the grid voltage there should be even higher. But I do not understand how V4 works. 
The grids are biased at 34 and 33 Volts.
I guess to get this little monster in working condition a lot of caps will have to be changed and the electrolytics will have to go but should I shotgun all the others to.
Also where the resistor got hot the chassis looked pretty baked and something was done to the tube socket closed to that resistor for reasons I don't know. Everything else in the amp looks pretty original. When you switch it off the filter caps hold the charge, so maybe they are not the culprit and the hum seems to be 50 Herz not 100 Herz (i live in millimeterland).
Any hints on what to look at are welcome, I will use a light bulb current limiter of cause, but what could make the output tubes draw excessive current?

[Williamblake]

https://el34world.com/charts/Schematics/files/Soundcity/Soundcity_120_miv.pdf

[Williamblake]

Also this amp has a standby switch from hell but I guess this is by design. Could I put a large resistor across it to cut down on the arching?

[shooter]

I wouldn't worry to much about the STBY switch, just leave it on n use power switch til it's fixed 
I'd pull ALL the tubes, get the PS rebuilt and working GOOD.  That should keep you busy for a few hours 

[silverfox]

Then bring it slow with either a light bulb limiter or Variac.


silverfox.

[Williamblake]

I will be doing that, ordering caps and stuff right now. In the meantime this is what I found online about servicing that amp.

http://www.iskrem.org/web/?p=300
http://www.chambonino.com/work/soundcity/city5.html
https://el34world.com/Forum/index.php?topic=10820.0
https://www.talkbass.com/threads/sound-city-b120-mkiv-restoration.779426/
https://www.reddit.com/r/GuitarAmps/comments/aiq4xb/so_ive_acquired_this_sound_city_120_could_use/

The talkbass thread is very detailed and mentions changing the rectifier diodes. They have to be partially unsoldered anyway, maybe I replace them, too? But what are they and what to replace them with? It's not mentioned in the schematics. Sorry I let Me Blurrycam take the picture.

[Fiat_cc]

The last big bass amp I did running 6 x 6CA7/EL34 type tubes used 1N5408 diodes.  It was running plates at 750V, so I am sure they'd be adequate for your rectifier.

[pdf64]

These amps are horrible, with some Sound Citys I've found that the fabric sleeving used over wire links can fail and become slightly conductive, causing all manner of crazy stuff.
Plus the tone control system is awful.
Such a shame as the iron is excellent.
Just gut it and rebuild it into a proper amp.
See gldtp99's comments https://www.thegearpage.net/board/index.php?threads/sound-city-120.2062870/#post-28870122

[Williamblake]

So this sat aside quite a while but the powersupply and bias is new and back to stock. The 100Ohm screen dropper was replaced by a wire once but maybe after one tube had died a screen resistor and the dropper and some cables burned. 2Ohm resistors were added between Pins 1,8 and ground. So i will check bias without tubes next and if everything runs fine the crackling mid pot and the coupling caps get inspected. I do have an attenuator build for just that but i expect reigning fear on my neighbours even at -20dB. There are a lot of Soundcity120 threats and in this thread it has been mentioned, too , to step away from the preamp. Its for a bass player and what Hiwatt or other circuit would be usefull to convert this to?  I dont want to get rid of the crackling only to give back an amp that could be soo good but still is a Soundcity120?

So i tried readind the other thread again.
https://hiwatt.org/Schematics/DR_Pre2Input.gif

[pdf64]

The bias supply of Sound City amps, especially earlier 70s models, is inadequate, and even with the bias trimmers adjusted to the greatest magnitude of applied bias, the power tubes idle way too hot.
The best way to resolve this is to convert the bias supply to s voltage doubler.

[Williamblake]

Thanks again.

I haven`t checked voltages without tubes, yet but am prepared to be dissapointed now.

I went through the amp with contact cleaner and measured resistances in windings and resistors  to double check and get a little familiar with the amp and noticed  the reverb in and out jacks in this amp are wired differently than in both Soundcity 120 Mk IV schematics available.

So in this amp the plate feeding the loop goes to send-tip only and with something plugged into Reverb-in this input resistance than would be the only resistive load of that tube behind the coupling cap.

The 0,15uF capacitor is across the the reverb out tip-switch so this cap would always connect in to out. With nothing pugged into both jacks the cap is shorted. You could insert an empty plug into Reverb-out  and the preamp would still be connected via that cap if nothing is plugged into Reverb-in.

I quadruple checked this as the schematics are a joy to look at and so is the wiring in this amp and also i don't see the sense this makes which can only mean it has something to do with the negative feedback happening in the following gain stage.

The Reverb-out-tip goes via 1M to the junction of the return stage's cathode resistors just
like in the L/B120 Mk IV schematics. Label says Model Nr L.120.

Little difference may this make if i change the whole preamp but i am also not sure about the 1,8 Ohm resistor between groung and HT secondary, it`s a high power resistor and would not be of any help in case current rises too high. It`s a little burned in that seems to bee somehow related to the fire that happended where a screen resistor once has been. Funnily the tubes in this amp are Siemens, maybe this is a another bad sign after all?

The diodes and caps in the power supply are replaced now and some dropping resistors, too.

[Williamblake]

Starting a new post to make it easier not reading every superflous detail.

Wouldn't it be a good idea tho get rid of the 1.8 Ohm resistor connecting ground to the secondary HT winding? Thinking again in a perfect world it might but it already saved my as when i should not have switched it on.

I don't have any spare EL34s i am willing to put into this amp, yet, so i would like to check it -  once the bias is adequate - with two tubes (push-pull), connect an 8Ohm Speaker and set it to 16 Ohm OT output. Bad Idea?

I have EL34's pin 1 and 8 connected and going to ground via a 2 Ohm resitor. Should Pin 1 go to ground directly?

So i checked without tubes and have -35VDC Bias, heaters are 6,8VAC and the light bulb indicator only lights shortly when turning on or stepping up the voltage. B+ was at 470VDC.

It was also mentioned somewhere else raising the cathode resistors to 100 Ohm to have adequate bias was someones solution and if i look at the EL34 datasheet it states -32VDC for 375VDC plate which would make it a tight fit on paper.  I wouldn't feel bad to try an easy way out first. But calculating this is just 4VDC less so i will be stepping up the bias now.

[SoundCity85]

The bias supply of Sound City amps, especially earlier 70s models, is inadequate, and even with the bias trimmers adjusted to the greatest magnitude of applied bias, the power tubes idle way too hot.
The best way to resolve this is to convert the bias supply to s voltage doubler.

My hobby of building (pre)amps started with getting a cheap Sound City PA120, and converting it to a Marshall 2204 preamp. I still have a stock L120, and then I recently rebuild another L120 into a Hiwatt mid 70s DR103 preamp. But I always left the power section untouched, besides changing the screen resistors and filter caps. I've read some things about the bias supply being unstable, but with my limited knowledge it is difficult to understand what is really causing the problems here. My two amps work good, but were not really driven hard for long periods of time. Drifting bias and red plating tubes are something I would like to avoid, especially since I'm putting very good tubes in them (Blackburn made), and want to make them as reliable as possible.

So my question, your suggestion of the voltage doubler, how does it work it practice, and does it increase reliability? I seem to had no issues biasing the RFTs and Sovtek EL34s cold enough. If there are good enough reasons to throw out the entire bias supply, I would be willing to do so, but need more info in that case.

I don't want to drag this off topic, but the voltage doubler and bias supply seem to be of interest for the OP to get his unit back into good working condition. My suggestion is also to remove the L120 active preamp and go for the 4 hole mid 70s DR103 preamp.

Best regards Dominic

[Williamblake]

The voltage doubler would be about being able to set the plate dissipation to less than 100%. With the the factory bias set to minimum power you hardly get or get not the factory settings that are on the edge of what the EL34 can stand and fortunately to my understanding a failing tube will slowly be more and more resistive but unfortunately this may not always be the case. Meaning the poweramp as is is a failure waiting to happen. Begging to be corrected. This may not be true for everybody but if you dial the bias a tad less than -34VDV (which is the max range you get from factory) you are just grinding on your tubes and with six of them at hand, would that be necessary? Well who didn't know that? Will report contact to voltage doubler atm. // you exchange the diode for the cap and put it in front of the bias supply and call it the Greinacher circuit, the voltage will be nearly twice and i think you wouldn't have side effects from switching on and off but i haven't tried tis, yet.

[DummyLoad]

a friend and i worked on one of these amps about 10 years ago. the tone stack is active and the amp is/was nothing but a noise maker. PS buzz and hum from the active tone network. pure needlessly complex garbage. IIRC the one on my bench was the mk IV. we replaced the output tubes, a couple of questionable e-lytics then sent it on its way, after we spent a couple of days looking for a fix for the buzzing/humming: come to find out much later, that was the norm for these amps from others. we then started referring to it from then on as the soundshitty 120.   


--pete

[Williamblake]

I must admit i was somehow reluctant to go for it when gutting it was first mentioned but i am slowly getting over.

Just found out there is a voltge doubler by Merlin:
http://www.valvewizard.co.uk/bias.html

[pdf64]

...Wouldn't it be a good idea tho get rid of the 1.8 Ohm resistor connecting ground to the secondary HT winding? Thinking again in a perfect world it might but it already saved my as when i should not have switched it on...

I guess it got included through necessity - maybe start up surge currents are too high without some current limiting?

...I don't have any spare EL34s i am willing to put into this amp, yet, so i would like to check it -  once the bias is adequate - with two tubes (push-pull), connect an 8Ohm Speaker and set it to 16 Ohm OT output. Bad Idea?

Yes, bad idea, as that would reflect a very low impedance load back to the EL34. Amp set to 4 ohms and an 8 ohm load would be better, but, as it's a 6 x EL34 arrangement, still lower than the designer intended.
Plus the HT will be rock solid, whereas guitar amps usually rely on sag at high power outputs to keep the stress on the power tubes within acceptable limits.
Point being that it should be ok at idle (assuming that the bias can be set suitably) and lower power output levels, just don't push it to high power output, and certainly don't crank it.

...I have EL34's pin 1 and 8 connected and going to ground via a 2 Ohm resitor. Should Pin 1 go to ground directly?

Ideally yes, but 2 ohms is negligible. But the schematic shows 68 or 22 ohm resistors between cathode and 0V, g3 direct to 0V; what's going on?

...I've read some things about the bias supply being unstable...My two amps work good...
...I seem to had no issues biasing the RFTs and Sovtek EL34s cold enough...

What plate or cathode current do the EL34s in your amps conduct at idle? I don't think that the stock bias supply is unstable, just it can be insufficient for some tubes. If it can be adjusted to a reasonable level, then there's no imperative to change anything.

Full disclosure - I've never worked on a SC 120, only a few 50 Plus. Of those, some needed a voltage doubler, others were borderline ok as stock, but I change them to a doubler anyway (unless requested not to), because if higher gm EL34 happen to be fitted later, then the bias would be inadequate.
For voltage doubler circuits, see https://en.wikipedia.org/wiki/Voltage_doubler
The Greinacher is easy to implement as a mod, because one leg of the bias winding stays connected to chassis 0V. It's only half wave, which isn't ideal but it's not an issue in this application, as the loading is very low.

Note the Valve Wizard schematic for the appropriate orientation of polarised ecaps, as it's confusing / non-intuitive.
The full wave Delon circuit is theoretically better, but a little more involved and so more work and complexity to implement it as a mod.

[SoundCity85]

Thank you for this very good info.

I will measure current again one of these days. If I recall correctly I measured plate voltage of around 480V and around 30 mA on my TAD Bias tool.

[pdf64]

...I will measure current again one of these days. If I recall correctly I measured plate voltage of around 480V and around 30 mA on my TAD Bias tool.

Yes, it’s probably worth checking idle current once in a while. If the bias supply can get the current down there, then it’s not worth messing with it. When it comes time to retube, that may change, so review things then.

[Williamblake]

Thanks pDF64 for not letting this result in a pile of smoke. Doing the footwork now.
// and thanks to silvervfox, shoother, Fiat_CC, Dummyload and SoundCity85, too. Each of your replies helped me.

[SoundCity85]

...I will measure current again one of these days. If I recall correctly I measured plate voltage of around 480V and around 30 mA on my TAD Bias tool.

Yes, it’s probably worth checking idle current once in a while. If the bias supply can get the current down there, then it’s not worth messing with it. When it comes time to retube, that may change, so review things then.

As I'm so happy with the FX loop, thanks to the people of the forum, I replaced the sovtek with Xf3 Mullard and now checking bias. I can get them down to around 23mA. The sovteks were running at 40mA. This means I will not make the voltage doubler at this point. This should be an amp mostly for recording purposes

[Williamblake]

Is there a need for two bias pods? I want to take the Valvewizard voltage doubler bias circuit and am a bit confused about the capacitor at the bias output (wiper) but this is where a 100k resistor would connect to the output of the phase-inverter coupling caps?

Anyway i dicided differently and just added a diode and cap in front of the bias circuit as there was no space for a seperate new bias board (,yet).

So now i have -45V DC to -78V V DC available at each bias pot which would bias the EL34 too cold. I would lower the idiot resistor marked in the schematic to get to a useful range and i guess i wouldn't want to have more than -34V DC available.

Pins 1 and 8 on the output tubes where connected to ground directly and that looked original.

Rebuilding this starting with the rectifier layout would have been clever as the new diodes are too short and the two storey poles are a bad joke and what not but i did not want to get confused with all the black wires hiding beneath the poles …

[Williamblake]

My question beeing: The voltage doubler increased the load on the bias winding and lowering the idiot resistor would even more do so. Maybe i better put a 10k resistor in series with the input of the bias pots?

[pdf64]

... Maybe i better put a 10k resistor in series with the input of the bias pots?

That’s what I do. Sorry, I should have mentioned it before.

[Williamblake]

Thanks again PDf64 for checking back on this. I dont mind the extra mile if there would be any at all. I disregarded your advice about regutting the whole thing in the first place and there is not much you could do about that.

Speaking of amps i now do wonder if this is a seperate bias winding or just a tap on the secondary, the voltages become adequaute but still i have to think about that.

// or even better i'll ohm it out tomorrow. Stupid lovely amp. I play electric with a plek, maybe 200W will teach me.

[Williamblake]

So i got confused about the bias voltages i got and bent on the turret board and got funny resistor readings in the bias circuit and started moving things around. It is really hard to get the solder of the turrets with wire still connected and i did some bad joints. I will be using the last row for grid and screen resistors only once i get the old circuit out of the way but am still planing to try this with the original circuit. The bias readings were funny because i forgot the peek sensing cap. From the picture it looks like i forgot both caps but i didnt. I dont know why i hesitaded drilling into the chassis, the next time i move stuff around, i will.

I get -32 to -47 VDC bias, this looks good?

[pdf64]

...I get -32 to -47 VDC bias, this looks good?

From the triode chart on p8 of https://tubedata.altanatubes.com.br/sheets/129/e/EL34.pdf it looks like that range should be ok, though the facility to get a tiny bit more negative may be handy with very high gm tubes. You'll have to check how it works out in practice, with the tubes you use.

Is that the HT rectifier FWB right next to the bias supply? I'd aim for a bit more separation between them. The resistors between the preset wipers look like they're joined together? If so I can't match that with the schematic.

[Williamblake]

The 132k resistors go from the bias wipers to bias pot input to protect against wiper failure.

So i felt lucky and brought this up on a variac with a light bulb meter and kept in mind that putting it into standby in that configuration would raise the heater voltage. Almost right from the start i did.

I left the bias to max negative and checked out the Siemens tubes that came with the amp and measured 5 to 11 mV DC across the 2.2 Ohm cathode resistor. So maybe the tubes still have some life? I checked the three EL34s i got from somewhere else and they measured 3mV DC each.

All this was done at max negative bias. So i should get the bias range more negative but it doesnt look too bad.

The layout will be changed due to bad durability with just one mount and i will keep in mind to increase the distance between the circuits.

Next step planned is to do the same thing again with a tad more bias voltage. I will put in pairs again and have the output set to 4 Ohm with an 8 Ohm load.

I thought i would hear thumping when turning this off but i didnt. Maybe i will when i increase tube current.

This feels like a big step forward from the last time i switched it on (see first post) , thanks for all the help.

[Williamblake]

So i did the same thing again, putting in two tubes a time but without the lightbulb and monitoring the heater voltage to get real live values at max negative bias and one tube was letting a screen resistor burn. So this tubes screen resistor shorted and the screen resistor was replaced but the tube wasnt and thats exactly what the chassis looked like when i opened it.  (Somebody had put in a 1k 12W resistor on top of a cinder that once whas original circuit.)

I will triple check the remaining tubes with the left over tube sockets before replacing the screen resistors with 1k 2W metal film.

[Williamblake]

By the way, i first thought whats that sound when switching on the bad tube and turned it off but then i was like well finally some hum only to notice the sound was emitted from the screen resistor which at that point started burning some. So i guess it was not mains frequency hum it was just the screen arcing once enough voltage was applied.

[Williamblake]

Guess i was wrong, it was the screen shorting to the heater wiring.

[Williamblake]

As i am rebuilding it i thought i no longer use the chassis as ground but will have a poweramp ground, preamp ground and ground the chassis at the input.

[Williamblake]

Try not to laugh.

[Williamblake]

And never mind me asking about 1k screen resistors, i do read the comments but i i am a slow learner, thats all. So this is going the DR103 way and i will have 100 Ohm screen resistors. 1/4 should be ok behind that 470 Ohm 10W resistor? I did calculate it and to me it seems adequate to let them act like a screen fuses. Idle screen current is 4mA and full pull is 25 mA so i calculated for 15 mA which makes much less (1/10) of a 1/4 W resistor to me. Sorry, it's late but 1/4 W 100 Ohm screen resistors seems reasonable to me. Not just because i have them at hand. Beging to stand corrected.

[sluckey]

You'll be fine as long as you keep using those dead EL34s.   

[Williamblake]

Thats even worse than i anticipated, i thought some would do fine once i turned the bias up. The ones giving the least current even have fancy wings. Thank god they were cheap. But once this is a non flaming amp there will have to be good good tubes and spares, too.

[Williamblake]

And i dont know if they are really dead, when i turned this amp on the way it arrived the tone control crackle was like a running jet engine falling down some stairs but the way the cookey crumbles they probably are. Thought they were at cutoff at -47 VDC.

[Williamblake]

Giving this some of the old back and forth.

[Williamblake]

The bias circuit could have much less wiring on the back but i am happy i dind't break the pods in the assembly. Found meself some power amp groud, too.

[Williamblake]

Finally some progress.

[pdf64]

...i will have 100 Ohm screen resistors. 1/4 should be ok behind that 470 Ohm 10W resistor?

I was sceptical but from P = I squared x R, a 100 1/4W should be good for 50mA.
Which seems well above what an EL34 g2 should be able to draw.
Whatever, they should have a flame retardant coating

[Williamblake]

They are spareholders, i have 5W resistors on the shopping list.

[SoundCity85]

...Wouldn't it be a good idea tho get rid of the 1.8 Ohm resistor connecting ground to the secondary HT winding? Thinking again in a perfect world it might but it already saved my as when i should not have switched it on...

I guess it got included through necessity - maybe start up surge currents are too high without some current limiting?

...I don't have any spare EL34s i am willing to put into this amp, yet, so i would like to check it -  once the bias is adequate - with two tubes (push-pull), connect an 8Ohm Speaker and set it to 16 Ohm OT output. Bad Idea?

Yes, bad idea, as that would reflect a very low impedance load back to the EL34. Amp set to 4 ohms and an 8 ohm load would be better, but, as it's a 6 x EL34 arrangement, still lower than the designer intended.
Plus the HT will be rock solid, whereas guitar amps usually rely on sag at high power outputs to keep the stress on the power tubes within acceptable limits.
Point being that it should be ok at idle (assuming that the bias can be set suitably) and lower power output levels, just don't push it to high power output, and certainly don't crank it.

...I have EL34's pin 1 and 8 connected and going to ground via a 2 Ohm resitor. Should Pin 1 go to ground directly?

Ideally yes, but 2 ohms is negligible. But the schematic shows 68 or 22 ohm resistors between cathode and 0V, g3 direct to 0V; what's going on?

...I've read some things about the bias supply being unstable...My two amps work good...
...I seem to had no issues biasing the RFTs and Sovtek EL34s cold enough...

What plate or cathode current do the EL34s in your amps conduct at idle? I don't think that the stock bias supply is unstable, just it can be insufficient for some tubes. If it can be adjusted to a reasonable level, then there's no imperative to change anything.

Full disclosure - I've never worked on a SC 120, only a few 50 Plus. Of those, some needed a voltage doubler, others were borderline ok as stock, but I change them to a doubler anyway (unless requested not to), because if higher gm EL34 happen to be fitted later, then the bias would be inadequate.
For voltage doubler circuits, see https://en.wikipedia.org/wiki/Voltage_doubler
The Greinacher is easy to implement as a mod, because one leg of the bias winding stays connected to chassis 0V. It's only half wave, which isn't ideal but it's not an issue in this application, as the loading is very low.

Note the Valve Wizard schematic for the appropriate orientation of polarised ecaps, as it's confusing / non-intuitive.
The full wave Delon circuit is theoretically better, but a little more involved and so more work and complexity to implement it as a mod.

Sorry to hijack this topic, but I found something here that interests me a lot. I've been breaking my head for a few days on this matter. When cranking the amp on an OX load box/speaker sim, I had red plating mullards on 1 side. Luckily noticed this fairly quickly, and stopped. On the bench I measured currents on the TAD bias tool that were reaching close to 200 mA. I don't think this is good for the power tubes :-)

I exchanged the 100 ohm resistor by a 10H choke.

Only thing I did so far was add again 250 ohm (4x 1K 5W in parallel) in between the choke and screen grids. Now on the scope I notice the clean headroom of the power section dropped considerable. But I guess it's still not a safe amp to crank. Any ways to really solve this issue?

[Williamblake]

I think this a contribution to the general topic and not hijacking. Why are you not using 1Ohm 1% 1/4W sensing resistors, it makes things very easy and safer, too. What is your bias? Dual? What is your screen grid power supply exactly, meaning shared and non-shared resistance? Do you set bias at idle or with strong signal? How many power tubes are you using? What is your output transformer? And what is the point of creating a beast like this to put it on a dummy load? No offense, but there are a lot of reports of doing exactly this and it went wrong. Especially when setting the bias with no signal applied.

[Williamblake]

Ymmv but it proved very convenient and reassuring to me to have a sheet to put my measurements into. Cant post .ods files, hope this works.

[pdf64]

…Do you set bias at idle or with strong signal? …

A good criteria for assessing the suitability of a bias setting is the anode dissipation at idle, ie that it’s in the Goldilocks zone of not too hot and too cold.
It’s useful to scope an amp’s output at various signal levels, using both resistive and inductive loads, to make sure the amp is working correctly.

[pdf64]

…
Only thing I did so far was add again 250 ohm (4x 1K 5W in parallel) in between the choke and screen grids. Now on the scope I notice the clean headroom of the power section dropped considerable. But I guess it's still not a safe amp to crank…

Why are you concerned that there’s still a problem?

[coribl1967]

Hello everyone,
New to the forum, so don't mind.
I need help, suggestions...
I got a Soundcity 120MK4, but it is in very bad condition, without an output transformer, most of the elements. I would like to do something for myself, I want an excellent clean tone and that it perfectly accepts processors. I would keep all 6 pieces of EL34 on the output because I like it loud, I got the output transformer from DR201 and JJ tube EL34. If you have any suggestions for the future, please post them here. Thank you!

[tubeswell]

Hello everyone,
New to the forum, so don't mind.
I need help, suggestions...
I got a Soundcity 120MK4, but it is in very bad condition, without an output transformer, most of the elements. I would like to do something for myself, I want an excellent clean tone and that it perfectly accepts processors. I would keep all 6 pieces of EL34 on the output because I like it loud, I got the output transformer from DR201 and JJ tube EL34. If you have any suggestions for the future, please post them here. Thank you!

I wouldn’t begin by trying to revive a 5 year old thread. Start a new thread.

[Williamblake]

Also what is "processors"? The amp as documented in this thread was actually loved by the base player it was given to. He uses a lot of pedals but he says he doesn`t need any pedals with this amp to get the sound he wants. Unfortunately it stopped working, no smoke though. Has to go back to the bench.

To answer the question: If you do no not have the output transformer, this thread is not for you. It was a shitty Soundcity amp with the guts to turn it into something beautifull. But maybe you could build the preamp with a different power amp? This is what i am thinking right now. Also, folks, don´t be like me, drop the effects loop.