Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: SleepLess on October 26, 2011, 07:51:36 am
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Hi!
As this one will be staying with me and I have almost unlimited budget to build it I only want the very best. What would you guys suggest as far as transformers go? Have you got a brand in mind? If you also have other recommendations to make concerning other parts (resistors, caps, whatever...) please don't refrain! Just bear in mind that I'm in the EU so the PT has to have a 220, 230 or 240V tap.
Thanks!
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Speaker: Weber 10F150-T (assuming you can get Weber speakers)
There's a long thread in the Archives which may be useful. A search here will turn up lots. A bunch of us built Princeton Reverbs in the 2006-2008 period.
I built two Princeton Reverbs, one with Mercury Magnetics iron and the other using Hoffman's. So similar any perceived differences in sound are just that. However, Hoffman's iron was much less expensive. Don't know if his PT has 220 VAC tap though.
Are you locked into using the vintage Fender layout? If not, F&T filter caps are an excellent choice for the power rail IMHO. Mallory 150 or Xicon coupling caps.
Frankly, spending extra Euros on "high end" components doesn't do much IMHO except for speaker, cab, and output transformer.
Hope that helps,
Chip
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Speaker: Weber 10F150-T (assuming you can get Weber speakers)
Yes I can, but I'll put the PR in a headshell and use it with a cab loaded with an EVM12L, that's settled...
There's a long thread in the Archives which may be useful. A search here will turn up lots. A bunch of us built Princeton Reverbs in the 2006-2008 period.
I built two Princeton Reverbs, one with Mercury Magnetics iron and the other using Hoffman's. So similar any perceived differences in sound are just that. However, Hoffman's iron was much less expensive. Don't know if his PT has 220 VAC tap though.
Well his store says that he only carries 110V versions so I have to be looking somewhere else. It would have ben my choice though to choose Hoffman's stuff... Oh well...
Are you locked into using the vintage Fender layout? If not, F&T filter caps are an excellent choice for the power rail IMHO. Mallory 150 or Xicon coupling caps.
Absolutely not, see I'm already changing it a whole lot with a headshell and a 12" speaker... I have already tried SoZo blue caps previously and they sounded great, but since I never heard the Mallory 150 I can't really tell the difference. One sure thing is that the Blues look better... lol
Frankly, spending extra Euros on "high end" components doesn't do much IMHO except for speaker, cab, and output transformer.
Mmm... OK. The speaker and cab are decided upon already, so I just need the trannies now...
Hope that helps,
Chip
It does help, thanks a lot Chip!
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Have you guys ever tried the ClassicTone transformers? I tried one in a 5E3 and it was great. Any feedback on their PR versions?
Thanks!
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yes, and they're fine. For components you could buy higher-end pots but you won't hear the difference, you will feel the difference when turning them and they may last longer in the end. Use a Hoffman board, not the original style paper-type boards that come ready made and that can be conductive. Another important thing that money can buy "better" are the tubes you put in. Almost as important as the speaker for hearing characteristic differences.
Things to concentrate on that money can't buy but are also very important are proper layout, lead dress, and grounding. These can render the other stuff pointless if not done correctly because what difference do they make if the amp oscillates, has parasitic oscillations, 60hz humm, etc...or worse - an electrocution waiting to happen.
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Which country are you in, if you don't mind me asking?
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Which country are you in, if you don't mind me asking?
No problem... I'm in France.
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The bunch PRs that were built a few years back were using the mods and schematic etc from Hotblueplates, and the layout for a turret board was done by bnwitt (Barry Witt), if I remember correctly. I built one from that, and it came out great, even though I'm not a Fender fan, and I still have it. Only thing I did different was to use a 12 inch Weber speaker.
The thread for it should on here someplace yet .... :dontknow:
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So I think I'll go with Classictone trannies. They're a lot cheaper than the hype MM and seem to be at least as good. I'll let you know how it sounds when it's done.
Thanks for your input!
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+1 on spending money on tubes. Much more bang for your buck than hi fi caps, etc.
IMHO every individual amp will "like" certain tubes in specific positions. I've got a collection of new 12AX7s from Tung Sol, Shuguang, EH, Sovtek, Mesa, etc. plus a few NOS and ANOS to play around with. I have learned NOT to make assumptions about which tube will sound best before experimenting.
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Got the tube ground covered pretty well already...
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Don't skimp on a good PT, especially if you're in a 'euro-voltage' country.You want enough iron in the core to handle the inductance at 50Hz well. Not enough iron = short-lived PT. Some transformer makers of 'euro-voltage' PTs don't seem to understand this (still!) and produce cheaper small PTs that don' have the staying power. Beware of this.
See attached graph. Think of the area under the function line as the amount of inductance happening in each case. the blue line (230V 50Hz) has more area under the function line than the red line (110V 60Hz)
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Wow, this is getting real technical here... Thanks a lot but could you just say what specs the PT should be within then? What specs should I be particularly beware of? Thanks!
The ClassicTone PT has a Plate winding 550 or 630V CT @ 100mA and Heavier current capacity (100mA vs. 70mA). Would that be good considering your graph?
MM may be great as well but the total reaches $235 compared to $90 from ClassicTone... These prices exclude the Reverb transformer.
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The PT secondaries will need to be spec'd to handle the overall tube load. What I was talking about was the amount of iron in the core (for iron-core PTs). Ideally your euro-voltage PT should be about 10-20% bigger than an equivalent (i.e.: for the same secondary specs) US-mains-voltage PT . This will help it to keep cool while running, and therefore last longer. This is likely to have a cost implication (which is why I suggested 'don't skimp')
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Hammonds are good transformers for EU based builders, Classictone I've used as well. Also there's another Portugal based option for PR & most other Fender type PT's http://www.rhodeselectrics.com/TransformersPower.html (http://www.rhodeselectrics.com/TransformersPower.html)
I'm still waiting for a reply for Fender style PT's from an English transformer company, they have already made Super Reverb PT's but I'm more interested in 125P1B / 125P26A types. Postage from overseas adds a lot to the total cost of builds :icon_biggrin:
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I love Weber Signature speakers. I have a Sig 10 ceramic in one Deluxe clone with a small cabinet and a Sig 12 alnico in another with a larger cab. Both sound great once broken in. An added advantage is that they are so cheap, though that's not why I use 'em.
$30 for ceramic 10"
$45 for alnico 12"!!!!!!!!!!
Their power rating (25 watts) is just right for a PR.
Dave
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I love Weber Signature speakers. ...
$45 for alnico 12"!!!!!!!!!!
Their power rating (25 watts) is just right for a PR.
+1 I've got a Sig12 in my PR cloney thing and its awesome
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Hi.
I'm finally getting to this build and I've just received the parts. I bought MM trannies all over and the PT's reference is FBFPP/240. It has a Heater CT which is pretty uncommon (at least for me, it's the first Fender build tranny I have that has a HT CT).
So the question is easy: am I using it or am I leaving it and installing the 100 ohm resistors on the indicator lamp and the usual Fender stuff? And of course if I do use it, how, where, and what does it change?
Thanks a lot!
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It's probably easier to use the CT. I think Sluckey said he always uses the CT if available with no problem. Little less soldering, 2 less resistors. HTH!
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It's probably easier to use the CT. I think Sluckey said he always uses the CT if available with no problem. Little less soldering, 2 less resistors. HTH!
Yes I'd rather use it but the problem is how... Do I just connect it to ground and don't install the 2 100ohms resistors on the lamp or is there something else?
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Oh, sorry! Yes that's exactly it. Bolt it down with one of the PT mounting nuts. Don't install the 100 ohm resistors, you only use either the CT or the 100 ohm resistors to make the artificial CT. Hope I've explained clearly this time! :smiley:
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Got it! I just need to not install the 100ohms resistors and ground that HT CT to the spot where the resistors would have been grounded... :think1:
Thanks!
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The heater CT can be grounded at the same place/with the B+ CT is grounded.
Look in here for grounding info;
http://www.freewebs.com/valvewizard2/Grounding.html (http://www.freewebs.com/valvewizard2/Grounding.html)
Brad :icon_biggrin:
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Great!
Before switching it ON (the build is finished) I would need you to confirm the CE cap wiring (40+20+20+20uF). What puzzles me is that it hasn't got a ground lug unlike the JJ cap of same values... So does this mean that it's not grounded at all or is there a log that is both a filter and a negative lug? If it's the case it's the lug that has no marking (the three others have a D, a square and a triangle).
Here's a pic of what I've done... Thanks!!!
(http://img267.imageshack.us/img267/3567/mg2739.jpg)
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Finally found a picture of an original PR:
(http://jeangodbout.com/princeton/chassis_full_view.jpg)
The four outer twist lock lugs are bent over backwards and soldered directly to the chassis. I suppose I could do the same? Or is there a modern better way?
Thanks!
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The four outer twist lock lugs are bent over backwards and soldered directly to the chassis.
They did that to hold the cap can in place and to ground it at the same time. The can itself has the negative ends of all the caps, 4 in this cap can, connected to it internally.
You have a clamp holding the cap can in place to the chassis, so you don't need to solder the 4 outside lugs to the chassis. Just solder a wire to any 1 outside lug and run that to your main chassis ground. Use a nice heavy piece of wire, maybe a cut-off piece of wire from the PT. That's what I'd try first.
Make sure you know which of the inner 4 lugs is the 40uF cap. That is the 1'st B+ filter cap.
Brad :icon_biggrin:
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Thanks! I soldered a wire from one of the outer lugs to the chassis ground and the amp works perfectly! It's real silent even on 8!
This amp is beautiful!!!
Thanks!!!
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Great! :bravo1:
Now do we get to see some nice gut shot pics? :undecided:
Brad :laugh:
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Sure... Gut shots served:
(http://img651.imageshack.us/img651/2817/mg2731.jpg)
(http://img96.imageshack.us/img96/3093/mg2735v.jpg)
(http://img18.imageshack.us/img18/7518/mg2736.jpg)
:icon_biggrin:
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WOW! Very nice indeed! :thumbsup:
How about a pic of the back/top side of the trannys so we can see the iron?
Brad :icon_biggrin:
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Thanks. I didn't take any shots of the top... But I have Mercury Magnetics all over. I wish I could try Hoffman's trannies but I need 230V here and his are 110V period... And the less I multiply sources the less costly the amp is... I try to stick with 3 online sources max and it's already quite hard to stick to that...
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One more thing, you do have a light bulb limiter to use on 1'st start ups and testing old amps/power supplies for safety?
Here's a link, with thanks to Sluckey, to how to build one if you don't. They work great are inexpensive to build and have saved a lot of guys a lot of heart brake and $$.
http://home.comcast.net/~seluckey/amps/misc/Amp_Scrapbook.pdf (http://home.comcast.net/~seluckey/amps/misc/Amp_Scrapbook.pdf)
Brad :icon_biggrin:
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One more thing, you do have a light bulb limiter to use on 1'st start ups and testing old amps/power supplies for safety?
Here's a link, with thanks to Sluckey, to how to build one if you don't. They work great are inexpensive to build and have saved a lot of guys a lot of heart break and $$.
http://home.comcast.net/~seluckey/amps/misc/Amp_Scrapbook.pdf (http://home.comcast.net/~seluckey/amps/misc/Amp_Scrapbook.pdf)
Brad :icon_biggrin:
That's some really interesting read! I'll have to delve into this! Thanks a lot!
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Excellent looking build! You did a really good job, easily as good as the original blackface Princeton Reverbs (I've owned a few of them).
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Excellent looking build! You did a really good job, easily as good as the original blackface Princeton Reverbs (I've owned a few of them).
Thanks a lot!!!
The only thing that actually tickles me when I build Fenders (whether Tweeds or Blackfaces) is the grounding scheme choice. For Marshalls I use the Larry Star Grounding (learnt on the MetroAmp board) which is just perfect 100% of the time.
As for Fenders I'm still trying things: buss soldered across the pots, floating buss wire (like I did on this PR build), brass grouding plate, terminal strips. All my Fenders have different grounding schemes and I don't feel that they're perfect as such. There is always a moment when I ask myself "should I solder this ground wire here or there?" "Should the buss wire be grounded close to the input jacks or closer to the PT", "should the terminal strip be grounded here or there and which wires get connected to it or not"?
Grounding Fenders is the only field where I'm not 100% content of what I do...
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Very nice build Sleepless. :headbang:
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Very nice build Sleepless. :headbang:
Thank you bnwitt!
I'm currently off to another build, a 5F6A. I changed the caps value on the PR from 25uF/25V to 25uF/50V and changed the bias cap from 50uF/100V to 100uF/100V and removed the resistor. This little amp sounds great!
I'm also currently thinking about whether attaching the two 100 ohms resistors to the lamp or to the power tubes (between lugs 2 and 8 on one and between lugs 7 and 8 on the other...). I do that on a 5E3 but I don't know if it is recommended on a 5F6A...
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Very nice build Sleepless. :headbang:
Thank you bnwitt!
I'm currently off to another build, a 5F6A. I changed the caps value on the PR from 25uF/25V to 25uF/50V and changed the bias cap from 50uF/100V to 100uF/100V and removed the resistor. This little amp sounds great!
I'm also currently thinking about whether attaching the two 100 ohms resistors to the lamp or to the power tubes (between lugs 2 and 8 on one and between lugs 7 and 8 on the other...). I do that on a 5E3 but I don't know if it is recommended on a 5F6A...
Your PR build looks very nice!
If you are talking about the virtual center tap for the heater winding, there is nothing wrong with tying it to a power tube cathode but you're simply connecting it to ground in a fixed bias amp. The cathode on a 5E3 sits at roughly 22 VDC, not "0" VDC like a fixed bias amp. Using an elevated DC voltage for the virtual center tap ground can help with noise rejection. Not as important in a push-pull amp as a single-ended amp.
Hope that helps,
Chip
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OK.
Thanks for the kind words!
I have soldered the two 100ohms resistors to the power tubes (pins 8 and 2 on V5 and pins 7 and 8 on V4) instead of soldering them to the indicator lamp.
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Very nice indeed. Looks like it would have came from one of fender's best builders.
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Very nice indeed. Looks like it would have came from one of fender's best builders.
Thanks a lot!!!
Well, there's a bummer though: it looks good but the tremolo is not working!!!! How's about a Fender best builder??? :laugh:
So I need you guys to make this amp sound as righteous as it looks. Here's what I've done so far:
1. Replace V4 with two differnt tubes: to no avail.
2. Put both intensity and speed on 10: to no avail.
3. Check wires going to V4: all good.
4. Measures:
B+ is at 439V (pins 3 of the output tubes) with 230V wiring for 228V wall voltage.
Bias is at 16mA for both tubes (perfectly matched)
V4 pin 1: 255V
V4 pin 2: 0V
V4 pin 3: 2V
Intensity pot middle lug: -44V
5. Changed the 1M resistor to a 220K (one of Sluckey's tricks to increase the tremolo effect), this one, to no avail:
(http://img849.imageshack.us/img849/3572/prtrem.jpg)
The thing is that the first three V4 pins should be oscillating and they are not...
I don't know what to do.
Thanks!!!
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The thing is that the first three V4 pins should be oscillating and they are not...
Are you sure? Those voltages indicate that it is probably oscillating. Use your footswitch to turn the trem off. Does the voltage on V4-1 increase quite a bit?
Intensity pot middle lug: -44V
Sounds way high for a PR. Adjust the bias to set that voltage to about -35vdc and see if the trem works.
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Thank you Sluckey!
OK. I adjusted the bias and I now have -36.4V at the middle lug of the intensity pot. B+ is down to 413V. I can't go lower than that on the bias (I have a 27K resistor on the bias pot). Still not even the faintest sign of tremolo... :BangHead:
Thanks!
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Mmm... I have measured my bias which I had to raise in order to lower the intensity pot middle lug voltage. So what I currently have is:
414V B+
-36V at middle lug of intensity pot
25.7mA bias on the 6V6s
I remember that I once had a PR that needed a lower bias on the tubes (17mA) in order to have its tremolo work. The thing is that if I want 17mA on the tubes then I'm gonna have -44V on the intensity pot again, lowering one increases the other...
So what do I need to change/alter in order to have both 17mA bias on the tubes AND -35V on the intensity pot? I'm lost there... Maybe it would work then as my wiring looks all good...
Thanks!
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Well, there's a bummer though: it looks good but the tremolo is not working!!!! How's about a Fender best builder??? :laugh:
I think you're missing a resistor.
Look at the schematic fragment you posted when talking about reducing a 1M resistor to 220k. If you follow the caps from the plate to the grid of the oscillator, there is a 1M resistor which reuns from the junction of two of the caps to the cathode of the oscillator.
In the pictures you posted earlier, there should be a 1M resistor running from your ceramic disc caps, where the blue underboard wire attaches, over to the yellow wire going to pin 3 of the oscillator tube. I don't see that resistor in your pictures.
Add it, and the reverb should come on.
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I think you're missing a resistor.
Damn! You're getting good at finding that missing resistor! :worthy1:
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Hot damn! I was so concerned about my wiring that I forgot to look at my components!
So the tremolo is working now!!!
One thing though, I don't know if that's normal: the speed increases fine but from 8 to 10 it's like the tremolo totally disappears, is it because it is going so fast that the human ear can't discern the oscillation? Or do I have to alter something until I hear the trem at work even on speed 10?
Thanks, I love this board!!!!
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I think you're missing a resistor.
Damn! You're getting good at finding that missing resistor! :worthy1:
I've been taking notes on how you find amp problems with a good picture.
Sleepless kind of distracted us with a second picture that wasn't from this same amp, which did have the missing 1M.
One thing though, I don't know if that's normal: the speed increases fine but from 8 to 10 it's like the tremolo totally disappears, is it because it is going so fast that the human ear can't discern the oscillation?
You can best answer this. If the trem pulses seem to get so fast they blur together, it should be pretty obvious to you, especially if you back the speed down slightly and can hear individual pulses.
You can slow the trem down by making one or more of the three disc caps a larger value.
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But what are the chances of two people building two different amps with two very different layouts (although exact same trem osc circuit) omitting that very same resistor within 3 weeks right here on Hoffman's forum? And in each case you spotted the missing component immediately! That's gotta be worth a lot of 'ataboys'. You got my attention! :worthy1:
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Thanks!
But it's the same silly mistake I would make! Maybe that's why I find them... :laugh:
I've said for a while now the only thing that separates an expert builder from a novice is that the expert knows that when the amp doesn't work, there's a build mistake. So they don't do perfect builds, they find and fix the error faster.
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Hot damn! I was so concerned about my wiring that I forgot to look at my components!
So the tremolo is working now!!!
One thing though, I don't know if that's normal: the speed increases fine but from 8 to 10 it's like the tremolo totally disappears, is it because it is going so fast that the human ear can't discern the oscillation? Or do I have to alter something until I hear the trem at work even on speed 10?
Thanks, I love this board!!!!
Check your pot and see if it changes from position 8-10. If there is a resistance change, you should be able to hear it. It is a 3 meg ra pot and I have a couple that do not change much at the end of travel. The taper just seems to make them get very close to zero very fast as they are increased.
Also, that 1 meg resistor change drives me nuts. I put in a 220k, then a 270k then a 500k and back to 1 meg. Right now it is 330k. I think I am going to put a pot on the thing. It sounds totally different as I did put a raw mod in thanks to Slucky, but it seems to change. I do not hear as well as I used to either. With a mid control and raw there are some really nice tones I am getting, but the overall trem effect seems to change as well. In reality it doesn't, but a change in tone changes everything.
Your build looks great. Way better than a RI Bassman I repaired for a friend recently. Thin wire, cheap pots and broken heater trace on the PCB. SO yes, your build is better than what is coming from Fender.
Great job.
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I have the same problem with my bias vary term. When I turn up the speed it goes so fast you can't even hear it's on.
The fix is to increase the capacitance in the LFO by changing 1 or more depending, on how slow you need/want it to go, of the .01 disk caps.
The 3-C's/3-R's (+1 pot) that form the FB loop, from plate to grid, around the LFO tube, form a time constant that sets the over all speed. More capacitance (and/or resistance) increases this time constant, because it takes the cap longer to charge up, slowing the LFO down. The speed pot increases/decreases this by adding/subtracting it's resistance from the main TC setting. It acts like a _range_ control for the TC setting.
Edit;
Although I'm sure that changing the cap value will change the speed, I'm not sure I got the TC/cap charging thing right here as the reason? Just re-read about trems/LFO's in a G. Weber and a KOC book.
Weber says it increases/decreases the phase shift of the FB loop, KOC says it changes the frequency of the LFO. It might all be the same thing, just a different way to say it? I'm thinking the phase shift is set at a frequency or is what sets the frequency of the LFO? And it might be that the TC is what sets the phase shift and/or frequency of the LFO?
Never looked at it this way before, am I close?
Brad :help:
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Phase shift = whereabouts in time that the peaks/troughs of the sine/signal wave are.
Frequency = how close-together/far-apart the peaks/troughs are
(Amplitude = how high/low the peaks/troughs are)
And yes - in a LFO circuit you vary the speed/rate/frequency of the trem signal by varying the phase shift of the RC network. The phase inversion of the tube does the first 180 degrees, and the RC network between the plate and the grid does the rest.
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Thanks Pete.
Well alright then, I think I get it. :undecided:
Brad :icon_biggrin:
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I tried many different values out of curiosity after reading lots of info on the trem. Seems like it only shifted the speed to a different position. Meaning the tremolo sped did not really change, it was just slower when the speed pot was lower which in turn made it slower at 1 or zero, whichever you prefer. I did not get a wider range, however I did get a very slow effect which made it slower when full on.
I was attempting to widen the range, but had no success. I am sure it can be done, but it is beyond my conception.
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I tried many different values out of curiosity after reading lots of info on the trem. Seems like it only shifted the speed to a different position. Meaning the tremolo sped did not really change, it was just slower when the speed pot was lower which in turn made it slower at 1 or zero, whichever you prefer. I did not get a wider range, however I did get a very slow effect which made it slower when full on.
I was attempting to widen the range, but had no success. I am sure it can be done, but it is beyond my conception.
All of this is really interesting...
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Hi there!
I'm in the middle of a Super Reverb AB763 build and I purchased a MM FBFS-P40/100-240 PT. I hadn't noticed it from the website but this particular PT has a bias tap. Do you recommend to use it and if so how and where? What's the use of that tap anyway, does it add or take anything?
Thanks!
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I would use it. Just wire it IAW the schematic.
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OK. So it goes to the end of the 470ohms/1w resistor on the bias board right?
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No it does not!
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Yes it does.
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Yes it does... I've just checked it on the schematic + TAD layout...
Sluckey, does this bias tap add a biasing stability or something? I'm interested in knowing its purpose, pros and maybe cons...
Thanks!
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It's just another way to provide input AC voltage to the bias supply. No real pros or cons. Just different (from your PR). The PR was the bottom line Fender reverb amp and chose the cheap way to get bias.
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Awesome! Thanks Sluckey!
I'll open up a thread once the Super Reverb is finished...
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Sorry! I had the main board in my head when I answered that,not the 'bias' board.Duh! :m20
The trem WILL slow down by upping one cap in the trio.It works every time for me,but you cannot go too large or it won't oscillate.
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> changing the cap value will change the speed
> Weber says it increases/decreases the phase shift of the FB loop, KOC says it changes the frequency
An oscillator needs loop (output to input) gain greater than 1.000 and phase-shift of zero (or 360) degrees.
The tube gives gain of 50 and 180 degree phase shift.
We need a trick to add an additional 180 degree phase shift. We like passive tricks. They are lossy, so we must find one with less then 50:1 loss.
One R-C network has phase-shift of zero and loss of zero at infinite frequency, phase shift of 90 degrees at super-low freq where loss approaches infinity, and at some in-between frequency it has phase-shift of 45 degrees and loss about 0.707.
So you would think to use four R-C networks at their 45 degree phase-shift frequency. Loss is about 4:1.
We have gain to spare. Can we be cheaper?
Three R-C networks will give a frequency where phase-shift is 60+60+60 or 180 degrees. At this freq each R-C gives loss near 3:1, total loss near 27:1. We could afford 50:1, so this will work.
For a fixed-frequency oscillator, the number of R-C nets is not too important.
However we want to vary the freq where we get the 180 degree phase-shift and oscillation. Ideally we use a 3-gang pot. This is expensive.
Turns out that you can get a limited range of frequencies by varying just one of the three Rs. The loss increases, which means the oscillator may tend to quit at higher frequency. However with a good 12AX7 and 10:1 range of pot you can get over an octave of useful range, which means you can beat-mesh any tempo.
Replacing one cap is a quickie. It does upset the loss. It may be better to replace all three caps with the next larger value.
> I was attempting to widen the range
To widen the RATE range? Reduce the fixed resistor in series with the Rate pot; however at some point it just quits oscillating. Or becomes too slow to start. Tinkering the gain might find a wee bit more range, but hardly enough to notice.
The direct way would be to switch the caps. The un-clever way would use a 3-pole 1-throw switch to put caps across the existing caps (or not). Using same values (parallel the 0.01 with another 0.01) would cause an octave-down (half-rate) shift.
Another way is to find a 2-gang pot, to vary two of the trhee R-C resistors at once. For the knob to go "right way" this must be a Reverse-Audio taper. These are not common parts. (Straight-audio works if you wire it the other way and remember to turn clockwise for slower.)
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Hi.
Thanks for such a thorough answer! One question though as it is linked with the Super Reverb optoisolator: One of the two lower legs is soldered with a 10M ohms resistor. can I safely change this for a 8.2M ohms or not? What will happen? Less trem? More? Instability?
Thanks!
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I'm in the middle of a Super Reverb AB763 build
And you need to go ahead and start a new thread. People are responding to your old thread about the PR.