Well, i might have the preamp under control to my satisfaction, if the electrical store could get my order right. They've sent me the wrong thing twice now, so i still haven't been able to settle the resistor value equation. But that should be solved in a day or two.

What i can do though at the moment is tell you the codes on the heatsink transistors, which are TD526, then underneath that code is the code 01 E.  I'm assuming the input to the heatsink is on the left (viewing from amp front) and the output on the right. I will take some photos of the area later today.

The white gunk underneath those transistors that you mentioned previously is bone dry.  I don't know if that has any bearing on anything?

Thanks for the explanations and further advice. You have a real knack for explaining things in a way that i can understand!

Get back to you soon

Paolo

You know alot more about this stuff than me, so i'll just have to accept it was manufactured like that.  As far as i'm concerned though, it's been fixed, BY YOU, ha ha!

Well the main part anyway.  I still don't know what is causing the ghost overdrive/fuzz, and you didn't mention it in the last post. Unless you are calling this "Overdrive Grunge", in which case if it happens "further down the line", i'll just leave it, as any more messing around by me might damage the amp.

When you suggested changing the elecrolytic cap, i thought this would make the overdive happen, so that is why i said it didn't do anything.  I wasn't listening for changes in the mid/treble. Should i try replacing it again, once i've got the right value resistor in place.

In a way, the gain knob working in this mid/treble manner was a good thing as it contributed to the woodyness of the middle and the chime of the top end at low volume.  Some of that will now be lost in favour of a fixed overdive and an improved reverb (with new tank).  The gain knob will have to be on zero, to avoid the ghost overdrive coming in for clean tone with reverb.

Ideally, i'm hoping for the great clean tone to remain, with good reverb available to that clean tone. I don't use reverb with overdive so that shouldn't be an issue really. Then also i'm hoping for a nice range and sweep of overdrive from the gain knob (after i've found the right resistor value). Obviously, given the manufacturing limitations, these two things will have to remain strictly seperate to both work effectively.  If i get all that i'll be really pleased, and we can say we have made a great improvement to this amp!

Yeah, Phil has been the main guy focusing on the reverb issue, i might attempt his stand alone reverb tank one day.

Thanks for the explanation of the gain, the components and the resistor chart.  Very useful info. I've learned alot from this forum.  I even have some idea now of what is probably wrong with the excessive bass on my Fender Princeton Chorus. So keep an eye out for that post! I even have a schematic!

What does HTH mean at the bottom of the post Roly?

Hi Roly

Yeah i think we/you are really starting to solve this problem!  I just want to get the amp to sound how it should have done originally or better.  I disagree though that the gain knob was designed to not produce any gain! I think the fact that we can get a big overdrive sound now proves that it's always been there?   

I'm also learning alot from doing this. While i'm on the subject, could you explain what the electrolytic cap does on my amp gain and why you thought of changing it? I'd like to learm as much as possible. I still don't really know what causes the overdrive other than the resistor controls the amount.  I only know about diode and LED clipping from pedal mods.

Yes i probably had my fingers contributing to the ohm reading! I've included a picture of the meter i use. As you can see on the left, there are several settings for testing ohms and as i said sometimes i'm not sure what to set it on, but i think i'm getting the hang of it more now. Prior to problems with my amp i'd only used it to test the resistance of pickups and to test battery power.

The 467ohm resistor was blue with dark blue stripes.  I got sent some with some LEDs i ordered for a pedal mod.

Perhaps the real problem with the gain on this amp (as i've mentioned over on the reverb problem post), lies with the ghost overdrive, which is still there under the regular crunchy overdrive. It's like two guitarists playing the same thing through the same amp, one using a distortion pedal and the other on overdrive pedal where the batteries in it are dying and it's like a splatty fuzz tone that has a longer sustain than the first guy's guitar. 

This is also present in the reverb and increases when the reverb knob (and/or the gain) is turned. It's always been like that.  It's not present if the gain knob is completel off.  I'd rather have the gain working than reverb, so it's not a big deal but i'm hoping we can fix this issue also, once i get the right ressistor to set the gain at the right balance.  Do you have any ideas what causes the ghost fuzz? 'Phatt' seems to think it can't be fixed (at least in the reverb).

I'll definitly have to start saving old cicuit boards. It's a good idea.

I really appreciate all the time you've spent on this and the step by step advice.  You have a lot patience!

Paolo

If the ghost overdrive in the reverb depends on the gain stage, then if the gain stage problem is fixed it seems to me that the the reverb is also likely to be fixed.  It happened in another amp i had and it WAS fixed. If it doesn't, then so be it, but i'd rather look on the bright side! 

As the ghost overdrive artefact is also present under the regular overdrive, it is a problem that needs to be fixed, as the amp would not have been made to sound like that originally. It is a problem that can be fixed by someone who knows what makes the ghost overdrive happen.

I have several reverb pedals, such as the EHX Holy Grail and Boss Fender 63 reverb.  The holy grail is too dark, and the boss is a one trick pony and sucks tone while it's engaged! You can't get a Fender amp accutronics tone from either. The reverb pedal i have used for years is a cheap Behringer DR100. The 'Spring reverb' setting on it is terrible but the 'Hall' setting on low is very similar to the reverb in my Fender Princeton.  The 'Room' reverb setting is what i use most because it sounds like you are playing a fender spring reverb amp in a small room, which in the house is perfect. so you get the best of both, with no tone suck on or off. The whole pedal is only useful on a low level setting though. 

I was deliberating about the Digitech Hardwire RV-7, which has the same sort of features as the behringer but is a superior quality pedal. On demos on youtube (like from proguitarshop), the spring reverb sounded great but i wasn't sure about the room setting, which is what i'd use mainly.  I'll have to try it in real life.
At some point in the future i will probably look into building a reverb unit from your schematic Phil.

Paolo

Hi Phil

Even with a better reverb tank there is still the ghost overdrive going on in the reverb, which increases the more you turn the reverb knob. Besides, i'm only really borrowing that reverb tank from the Carlsbro at the moment. I would need to buy a similar new one.

I call this ghost overdrive because it is only semi there and haunts the sound which should be clear.  To clarify: it sounds like the normal reverb, but it's like someone is playing along with what you play in the backgound on a overdrive pedal where the batteries are dying and it's more fuzzy.  Everyone know that sound!?  C'mon, someone must have had this issue with their reverb in an amp over the years?

Since the Gain knob problem is nearing a solution, i'd rather have gain working than reverb if i had the choice.  Lifes too short for bad reverb!!  The ghost artefact is not there when the amp is just clean.

The real problem with this amp i suspect lies with that ghost overdrive, as that is also present underneath the crunchy overdrive i'm getting now from the gain knob. As the good overdrive is fading the ghost overdive/fuzz is still there.

For now i'm going to leave the reverb problem as is, until the Gain problem is completely solved, then hopefully the ghost overdrive might disapear from the reverb/ or be a seperate issue to solve.

Thanks to everyone who has been helping and commenting.  I'll update this post when any new deveolpments occur.  Please still feel free to comment though, if you have any advice on the above.

Paolo

JM - What i meant is that i don't need so much technical detail with suggestions because i probably won't understand it; conversely, i need SOME explanation along with the suggestion of how things will work so i can picture it in my mind. People seem forget i'm an electronics novice.

Anyway, good news and bad news on the reverb front:

Before i spring for a reverb tank (yeah you got it!) i need to know it will work WELL, not just work in the manner it does already (ie badly).  As i said, i have a few other old amps (Carlsbro's) that i suspected had Accutronics tanks, and just .. maybe.. a near enough input impedence tank might be lurking in there.  So i dragged out the Carlsboro Lead 100, and sitting inside was a type 1 Accutronics which is the 2 spring smaller tank. Designed for practice amps, a step down from the 3 spring smaller tank, but still USA Accutronics, so all good.

Well, i tested the input and output impedance  and .... it's virtually IDENTICAL to the Prince amp!! This is exactly what i needed, bacause if this works, i know a 3 spring will be even better. So i hooked it up to the Prince and there is a vast 500% improvement over the original 1 spring tank.  Not super lush but pretty good at lower levels.

Now the bad news. The same undercurrent of overdrive fuzz that was present before was still there when the gain knob was also turned up. (If you are following the gain problem post, you will know that the gain knob only functions as a volume with a strange barely audible fuzz gain in the background when turned up from 8-10 or so.)

Basically, i think i will be only be able to have gain OR reverb. I suspect that the artefact of ghost fuzz in the reverb will still be there when the gain knob problem is solved.  I say this because many years ago the reverb knob on an amp i had back then basically turned into a gain knob overnight.  The guy who fixed the amp back then told me what made that happen but i can't remember what he said, but that it had been an easy fix.  So i think that will be almost a third problem with this amp!

So at least i know that a different tank can be put in this amp and make a dramatic improvement, ableit with caveats at the moment.

As always i look forward to your comments and advice!

Paolo

Hi Callum

That Carlsbro amp is like likely to have a USA made Accutronics reverb tank in it also, which could be usefull for future projects.

If the amp has a Celestion speaker, it is likely a replacement from the original (unless it's a more modern Carlsbro GLX or something, in which case they might come with them) If it's from the 70's/early 80's, then the original speaker would more likely to have been made by either Fane or Mackenzie, which are great brithish speakers and highly sought after.  These were often unbranded or labelled with the Carlsbro name 'Powertone'.
I had alot of discussions with one of the engineers from the Carlsbro factory in the UK, who also used to run (a now defunct) Carlsbro website, where you could date the amps and there were forums, etc.

Another little known fact about Carlsbro, is that they took over production of H&H amps about 2-3 years after that company started. So most H&H amps are technically Carlsbros. One goes for big bucks, the other next to nothing. I have 3  Carlsbro amps from the 70's that i got for under £20 each.

Anyway, good luck with your project!

Paolo

Hi Roly

I've tried a few things from your suggestions with some positive results!

1.  I changed the electrolytic cap with a couple of the ones i had spare (22uf/10v & 10uf/35v, but this didn't seem to make any difference at all.  Eventually, after the whole testing session, i put the original back in as i don't think it was the problem?  Is this what you thought was the main problem?

2.  I took out the 820 ohm resistor and I tried a 467 ohm resistor. This didn't seem to make much difference.

3. I didn't have any resistors of a lower value, so i just went straight for a jumper wire. This gave the massive overdrive that i got when i used the EHX clean booster pedal before it. This was in the 'Boost' input, but i also plugged into the 'Normal' input and got similar results at a lower volume and reduced gain.  So now we know the amp works on the same basic principle as most amps with a high and low input.

4. From 1 - 8 on the gain knob, nothing really happens different from before (just gets louder), then the overdrive kicks in dramatically between 8 - 10. , with little scope for much fine adjustment.  I assume this is because there is no resistor, just the jump wire? 
The overdrive itself is pretty raw in a crunchy marshall distortion way, with an undercurrent of fuzz. There is artifacts in the sound at higher volumes, but this is probably due to vibration from the amp being open and not all screwed down. There i also a high pitched whine when using the headphone socket with the gain on full using the Boost input.

Some people would love this tone as is, but i need less (or the more scope to go from less to more) and a more gradual sweep on the Gain dial.  It's amazing how one tiny part can make so much difference!

I've sent off for some of the other resistor values you suggested, so i'll try those when i get them.

Only recently, i chucked out alot of old hi-fi equipment/ ghetto blasters that were partly broken.  Some good made in japan stuff from the 70's. I took out some electrolytic caps and normal caps and some other parts, but didn't take out any resistors because i didn't think i would be able to identify them, or even need them for that matter.

I really appreciate all the help and advice so far. Getting some results now!

Paolo

Hi

The thing with living in the UK, is when it comes to certain musical instruments or related products, the postage is often more than the actual item. This is the case with Accutronics reverb tanks shipped from USA. New Accutronics reverb tanks are seemingly only available from one dealer here in the UK, but the price only seems slightly higher than the USA price, and of course postage is minimal. Ss that is a viable option.  I was thinking the 8BB2C1B?

Phil - I'm assuming you mean the Belton Digi-log/ 'The Brick'?  I've come across this box in my recent research into reverb tanks. Also now available in some sort of pedal i believe.
This option would be far cheaper as they can be bought for about £10.  I think you have to have some kind of supporting circuitry and power supply though?  (Incidentally, i have an old K Kustom amp that has a small open 2 spring reverb tank made by Belton, and that does sound very good.... very Fender. I've thought about trying that but reverb tanks made for modern  non fender amps seem to have specific input ohms tailored to the circuitry of that amp.

Also, while looking into the reverb problem, i've come accross someone who changed the RCA reverb jacks to 1/4" jacks in a silverface fender and used an Alesis nanovervb as the reverb tank. Probably, a stupid question, but would this work or not work with a reverb pedal?

Everyone has been very helpful with detailed opinions and possible solutions. The thing is, that before i attempt to build ciruits and/or spend over £50 on an Accutronics tank, i need things explaining in a non technical language that i can understand, so i can get my head round it. I need to know i can do it before i slpash out on all the parts and tank.  I also need to know more of the fine details like i mentioned in an earlier post.
The main reason i need to know all this is because this is one of my favourite amps so i don't want to fry the electrics by guessing or not understanding! If you look at it from my point of view -  for example, suggesting i get a Belton Digi-log.  Say i get one and all i have is just a mystery box with no input or out put jacks. What do I with it?  I need to know how easy or difficult it is to connect it to the amp, and what else is needed.

Phil - Yes i am old enough to remember Vinyl records!! I have an extensive collection.  I also currently collect old soul and R&B 45's form the 50's and 60's, so i'm an active turntable user and have good gear. I understand sound, just not so much electronics and it's language.

Roly - I've seen those plates in amps before now you mention they are usually black. They sometimes look like a 3d comb.

I've used Servisol for years on the pots on all my guitars and amps. Super 10 is made for cleaning electrical components. They make dozens of different cans of cleaners and lubricants.  It works really well and i've never had a problem with it.  I was told that it was WD40 that was never to be used on guitar electronics as solvents in it corroded the plastic wipers. Maybe the guy above used the wrong type of Servisol.

Here is the Servisol company website with contact details if any one wants to check to be sure:

http://www.crcind.com/csp/web/functdisp.csp?lng=3&idx=1933341&country=GB&brand=SERVISOL&CSPCHD=0000000100003wkvjAxp000000WW8fmB$YPgQzJl9nImpUWg--

I was just looking on e-bay at reverb tanks and here is someone selling the exact tank from the Prince amp!  Has a few NOS units.  Apparently made by Tokai:

http://www.ebay.co.uk/itm/DIY-guitar-amp-reverb-tank-80s-NOS-Tokai-TA-35-made-in-Japan-limited-quantity-/250996691938?pt=UK_MusicalInstr_Amplifiers_RL&hash=item3a709193e2

Whatever you do, don't 'Buy it Now' (or ever)!!

Hi Roly

1. Measure the resistance between ground "Gnd" and point "A" while varying the gain control.  The resistance to ground at this point should vary between nothing and whatever the value of the gain pot is (a few k ohms?).

A: This reads from zero to 2.7 ohms while turning the dial.  The gain pot itself says B3K ohms.

2. Next do the same thing from ground to point "B".  In this case the resistance should go from the upper value found above, plus about 1k, to around 820 ohms.

A: At full clockwise it reads 820 ohms, then gradually gets into the 1000's as you turn it back to Zero. (I have to point out here that i always have a real problem reading the meter, as i'm never sure which setting to put it on in the ohms catagory. i don't know the difference between ohms and k ohms and stuff like that! The meter i have is also very basic).

3. Try replacing the electrolytic cap (shown in green circle in the top view) with the same value (this doesn't have to be exact, 10-20% more capacitance and/or voltage is fine).  Note value and post here as soon as you know.  This cap is polarised and must be replaced in the same polarity (use marking pen to mark on the board where black negative mark is on the cap before you remove it).

A: The only writing on the elec cap is Tracon and 10/16.

    These are the spare elec caps i have:   4.7 uf/25v
                                                        10 uf/35v
                                                        22 uf/10v
                                                        22 uf/50v
    Should i try any of those?

As for the mods, my playing style doesn't need loads of overdrive, as i like a gritty, open medium break-up overdrive. Sort of keith richards to george thorogood tone. So i probably don't need even more overdrive than the amp does already! The overdive i was getting with the EHX signal booster pedal sounded pretty good, a bit like my Fender tweed Bronco, but with it's own 'unique' 70's Japan Solid State touch!

Thanks for all the advice and lnks there Phil!

Alot of went over my head, and maths is definitely not my strongpoint!

The thing about schematics and me is that i can't relate a scematic to the real thing. Particularly if i haven't got the real thing or a photo of it.  For instance, with the reverb schematic, i can't tell if the finished thing is a stand-alone unit; or it goes inside the amp; or is it like a giant effects pedal that you plug your guitar into that way. Do the components go in a box beside the tank; do they go where the tank originally was in the amp; are they on a PCB, etc etc. I gather from reading between the lines, that it will go in the floor of the amp with seperate electronics box connected to the main circuit, but i couldn't tell this from looking at the schematic.
I like to use the analogy of a sheet of music, as i can't read music, but i can read guitar tabs because it looks like the 'real' thing, ie the gutar neck. 
Sometimes, when i see old valve amps that have all the components soldered side by side in a line (linear) fashion on a turret board, i think "I could probably build one of those" with some 'airfix' style instructions and a parts list.

Nevertheless i may give it a try at some point, as i don't know that the amps reverb will ever sound that good even with a new tank.

As you can see in the photos, the amps reverb tank only has one spring as i predicted.  It also looks to be undamaged. Though there is a hailine wire (see photo below) that comes from the end of the mount at one end and touches (but not soldered to) the base of the tank.  At the other end of the tank there is a similar wire, but this one is shorter and doesn't touch the base. Are these of any relevance? I tried connecting the short wire to the base so both now touching but no difference.  Also tried lifting longer wire but no difference.

The readings when disconnected are 215 ohms input and 210 ohms output.  In the photo's, there is also a polished metal plate behind where the reverb was, where some wires from the PCB are attched.  Any idea what this is?

The spare reverb tank i have is an Accutronics 4AB3C1B which is full size and has 6 springs. Straight off, this is too big to fit in the floor of the amp cabinet by about an inch. From your descriptions, it is also probably not suitable to be used in Rod's reverb circuit.  I'm also not sure that it is working correctly, as the readings are 1.2 ohms input and 40 ohms output, which is nothing like what it is supposed to be.  Anyway, i connected it to the amp to try it and there was a faint ethereal reverb and the springs 'boinged' when touched (along with the undercurrent of ghost overdrive i have previously mentioned).

The other reverb tank i had was from a 70's Carlsbro Stingray Combo.  I can't find it so i think i must have put it back in the amp (which currently doesn't work), but that was definitely full size and had either 4 or 6 springs.  I also remember that it sounder too mellow, dark and distant, but that's probably the amp circuit playing a large part. Anyway, again too large for the Prince amp. I have two other Carlsbro amps which i think have the shorter accutronics tanks.

As i've prevously mentioned, my favourite amp reverb is the Accutronics in my Fender Princeton Chorus.  This is a short tank with the code 8BB201B with 3 springs and medium decay.  If i had to buy a new one, this is the one i would get, as it sounds just right to me - bright, snappy and not too distant.  The Brian Wampler Faux Reverb pedal seems to nail this tone also.
(The Fender Princeton Chorus also has a minor problem with the bass, but i will do a future post about that!)

I generally only have a touch of reverb (or sometimes analogue echo, or mix of both) as i play rock'n'roll and blues based music and don't need epic cavenous decay. I also have the Boss Fender reverb pedal if i want 'excessive' wet reverb.

Anyway, i'm thinking that it's going to be impossible to get a tank that matches the input/output of the Prince amp(?), so i will either have to built one from the schematic at some point, or buy a pedal like the Wampler.

Let me know your thoughts.  Here's the photos.

Paolo

Hi

I have been trying to draw/trace the circuit around the gain area, which has took around 6 hours!, but i've just looked at the photos i took, and i think the x-ray pictures are actaully better. I think this will leave no doubt where everything is, and someone will be able to see it as a schematic. 

Roly - I will try and work through your suggestions shortly, but i might not have the components at hand to try some of the suggestions and will have to order them.

Anyway, i hope the new photos are helpful! If anyone wants any components or connections  identified more specifically i will try to see what is written on them or where they join. The ony thing i can't tell from when i was drawing it out was, where the silver metal towers are connected underneath.

I think this site is terrible for being able to view pictures! Each picture should have a scroll bar to move the view along, and/or show them full size when you click on the thumbnail.  The best thing to do seems to be to click on the blue file name under each photo and open them in your prefered image viewer and make your own copies.

I have also updated and put photos on the reverb problem post.

Paolo

Thanks for your input Phil. Yeah it might well be the circuit, but i've got to at least try a different tank in there.

I bought a Boss FRV-1 '63 Fender reverb pedal a few months back, but i find it only really useful for the full on surf tone reverb. It's not very subtle. I wish i'd bought the Digitech Hardwire RV-7 now as it has more options, and is popular as a back up to the real stand-alone tank among the surf band community.  Mostly though, i only use reverb sparingly and prefer a kind or room reverb for general playing, but occasionally need more for atmosphere, or surf tone.

That's interesting about the amount of springs, i'll have to try that out. By the way, the accutronics with 6 springs had 3 rows with 2 springs per row (or maybe it's 2 rows of 2 springs.  It's a few years since i looked at them).
I suppose long springs in a long tank like that needs some kind of support in the middle. It didn't sound no where near as good as the shorter tank in my Princeton though, far too distant and dark.

I'd love to build my own reverb unit, and have thought about it for a few years, but haven't had much luck finding any info on how to do it. How hard is it to build your own tank then Phil? Do you have a schematic for future reference?

This site is great i'm learning all the time from you guys!

Paolo