A few months ago I posted about converting an Ampeg V5 to a Hiwatt DR103. You can read the post here if you'd like.
Quick background: My friend/guitar player in my band bought an Ampeg V5 in hopes of having a cool variation on a 2203 circuit but we found out after purchasing (Reverb) that the previous owner had totally gutted the amp and modded it beyond recognition with all new iron. Rather than make it just another 2203 clone (the original iron would be hard to come by), we decided to turn it into a Hiwatt DR103 which is the amp he actually wanted all along.
This project certainly has been a labor of love but it's been pretty fun, too. I'm finally "done" with it and I'm running through initial tests. Last night it fired up dry just fine. Popped a Mullard CV4004 in V1, Gold Lion 12AX7s in V2 and V3, a Gold Lion 12AT7 in the PI, and Gold Lion KT77s for the power tubes. Before biasing I was seeing about 478V at the plates and after biasing to 39mA I was seeing about 450V and feeling pretty good about things. Hooked it up to an 8-ohm 300W dummy load with a 10X scope output and without anything plugged into the input I'm getting a 7Hz oscillation at about 93Vp-p. Very weird but I won't be able to troubleshoot this until later today because I've got a few other things to do first.
EDIT: I actually zoomed into the waveform on the oscilloscope and I'm actually seeing a 60Hz oscillation so I'm thinking there's a grounding issue. More to come...
I've attached some images to the post but here is the full gallery if you're interested. She ain't gonna win any beauty contests, that's for sure, but I'm pretty proud of it since it's my first real from-scratch build. If you see any obvious red flags, please feel free to point them out! Thanks for looking.
Ampeg V5 to Hiwatt DR103 Conversion Project
Moderators: pompeiisneaks, Colossal
Ampeg V5 to Hiwatt DR103 Conversion Project
You do not have the required permissions to view the files attached to this post.
-
Stevem
- Posts: 4750
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
1 others liked this
Re: Ampeg V5 to Hiwatt DR103 Conversion Project
93 volts P to P is over 1000 watts into a 8 ohm load, so your 300 watt load resistor should be burning up!
Is that the case?
I would start troubleshooting by yanking out preamp tubes starting with the first gain stage.
If one of those tubes being out stops it then you can zoom in more by shorting across plate load resistors which will kill the gain from that stage.
Build review wise I can tell you this.
Long grid wires going from the PI output blocking / coupling caps to the output tube grids are a flat out engraved invitation to a oscillation problem.
It may not look neat, but what you aways want in a build is to have any input grid wires as short as possible.
On my builds and mods in particular I put these caps that couple to output tubes right on the output tube sockets.
The reason being the audio drive voltage to the output tubes is the highest in the whole amp at this point and can bleed all over the place.
You should always think of any grid wire in a audio amp as a very sensitive antenna when thinking about a layout of a build.
To sum up, preamp plate leads can be long if need be, but input grid wires need to be short especially as gain levels go up and signal drive levels go up.
I see no need for 4 separate grid feed wires like you have to the output tubes.
Is that the case?
I would start troubleshooting by yanking out preamp tubes starting with the first gain stage.
If one of those tubes being out stops it then you can zoom in more by shorting across plate load resistors which will kill the gain from that stage.
Build review wise I can tell you this.
Long grid wires going from the PI output blocking / coupling caps to the output tube grids are a flat out engraved invitation to a oscillation problem.
It may not look neat, but what you aways want in a build is to have any input grid wires as short as possible.
On my builds and mods in particular I put these caps that couple to output tubes right on the output tube sockets.
The reason being the audio drive voltage to the output tubes is the highest in the whole amp at this point and can bleed all over the place.
You should always think of any grid wire in a audio amp as a very sensitive antenna when thinking about a layout of a build.
To sum up, preamp plate leads can be long if need be, but input grid wires need to be short especially as gain levels go up and signal drive levels go up.
I see no need for 4 separate grid feed wires like you have to the output tubes.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Ampeg V5 to Hiwatt DR103 Conversion Project
Nice looking build!
First thing to check is your global negative feedback (from speaker output back to PI). If the OT primaries are swapped, this may solve your oscillation. Simply disconnect the NFB wire to check if the oscillation goes away.
First thing to check is your global negative feedback (from speaker output back to PI). If the OT primaries are swapped, this may solve your oscillation. Simply disconnect the NFB wire to check if the oscillation goes away.
I build and repair tube amps. http://amps.monkeymatic.com
-
Stevem
- Posts: 4750
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
1 others liked this
Re: Ampeg V5 to Hiwatt DR103 Conversion Project
Good point!
I forgot that's this is the first thing that bites most people in the Ass in new builds.
I forgot that's this is the first thing that bites most people in the Ass in new builds.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
-
Reeltarded
- Posts: 10017
- Joined: Sat Feb 14, 2009 4:38 am
- Location: GA USA
1 others liked this
Re: Ampeg V5 to Hiwatt DR103 Conversion Project
It looks sweet!
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.
Re: Ampeg V5 to Hiwatt DR103 Conversion Project
I try not to let oscillations, especially of this magnitude, run for too long while I'm testing so I haven't really noticed the load getting very hot. I only run it for maybe 20-30 seconds to allow me to take a measurement and then I turn it off. That being said, I've also trained myself to not touch the load box in general while in operation because it does generally get hot.
Sounds good. I will do this.
OK, great advice, thank you. It makes sense to put the grid resistors as close to the tubes as possible. Not sure what I was thinking when I laid the board out. I will make this change across the amp, including on the preamp tubes unless you think that's unnecessary. However, one question: You mention putting the coupling caps as close to the tubes as possible, but I see some challenges for me to do that. If you view the attached image, I've highlighted some nodes on the schematic. Right now the green connections are the long wires, which you have pointed out as being bad. Could I make the yellow traces long? Or do you only recommend I make the blue traces long? I will do whatever it takes to make this build as good as possible so please tell me your strongest recommendations. Thanks!Stevem wrote: ↑Fri Jun 23, 2023 10:51 pm Build review wise I can tell you this.
Long grid wires going from the PI output blocking / coupling caps to the output tube grids are a flat out engraved invitation to a oscillation problem.
It may not look neat, but what you always want in a build is to have any input grid wires as short as possible.
On my builds and mods in particular I put these caps that couple to output tubes right on the output tube sockets.
The reason being the audio drive voltage to the output tubes is the highest in the whole amp at this point and can bleed all over the place.
You should always think of any grid wire in a audio amp as a very sensitive antenna when thinking about a layout of a build.
To sum up, preamp plate leads can be long if need be, but input grid wires need to be short especially as gain levels go up and signal drive levels go up.
I see no need for 4 separate grid feed wires like you have to the output tubes.
OK, I will try this, thank you!
Thanks!
You do not have the required permissions to view the files attached to this post.
Re: Ampeg V5 to Hiwatt DR103 Conversion Project
After looking at some wiring layouts, last night I moved the grid stoppers right onto the power tubes. I did the same for V1. Now the noise at the output is a steady 86.27Hz at 75Vp-p. So... progress? 
First thing I tried was removing the NFB but the noise persisted. I have yet to start popping tubes out to see what that yields.
First thing I tried was removing the NFB but the noise persisted. I have yet to start popping tubes out to see what that yields.
You do not have the required permissions to view the files attached to this post.
-
Stevem
- Posts: 4750
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Ampeg V5 to Hiwatt DR103 Conversion Project
Last edited by Stevem on Tue Jun 27, 2023 8:30 pm, edited 1 time in total.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
-
Stevem
- Posts: 4750
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Ampeg V5 to Hiwatt DR103 Conversion Project
Well Its time to start removing tubes to deactivate circuits and then replace them one by one.
Yank them all out but for the output tubes, do you still then have the issue?
Also something is very messed up in one way or another with what your reading for output voltage to your test load resistor.
It’s flat out 1000% impossible for that amps power supply and output tubes to produce 76 volts P to P Into any type load .
76 volts would be over 700 watts, so logic would tell you that if such was the case then in about 30 seconds both your OT and resistor load would be flaming!
Don’t bother for now in reporting back as to what voltage your seeing at the output jack when reading what your scope is telling you.
If nothing else please use your voltmeter set for ac to check what you have coming into the load resistor.
Yank them all out but for the output tubes, do you still then have the issue?
Also something is very messed up in one way or another with what your reading for output voltage to your test load resistor.
It’s flat out 1000% impossible for that amps power supply and output tubes to produce 76 volts P to P Into any type load .
76 volts would be over 700 watts, so logic would tell you that if such was the case then in about 30 seconds both your OT and resistor load would be flaming!
Don’t bother for now in reporting back as to what voltage your seeing at the output jack when reading what your scope is telling you.
If nothing else please use your voltmeter set for ac to check what you have coming into the load resistor.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Ampeg V5 to Hiwatt DR103 Conversion Project
I pulled all the preamp tubes and started putting them back in, going backwards from the PI (V4), and the noise returned when V3 was put back in, so I am suspecting something in the Presence/NFB circuit. Attached is the schematic.
I just disconnected the NFB and the noise went away so I'm going to swap the OT primaries to see what that does.
I'm measuring 35VAC with my multimeter at the output jack. I'll double-check the calibration of the 10X scope output on my load box.Stevem wrote: ↑Tue Jun 27, 2023 8:28 pm Also something is very messed up in one way or another with what your reading for output voltage to your test load resistor.
It’s flat out 1000% impossible for that amps power supply and output tubes to produce 76 volts P to P Into any type load .
76 volts would be over 700 watts, so logic would tell you that if such was the case then in about 30 seconds both your OT and resistor load would be flaming!
Don’t bother for now in reporting back as to what voltage your seeing at the output jack when reading what your scope is telling you.
If nothing else please use your voltmeter set for ac to check what you have coming into the load resistor.
I've always calculated the RMS power based on the non-clipped signal from the scope. I calculate the RMS voltage with the formula Vrms = (Vp-p)/[2*sqrt(2)]. I then use [(Vrms)^2]/Rload to get the RMS power. At full clipping, the signal is usually much bigger than the non-clipping signal so these equations would yield much bigger (and scarier) numbers, but I'm not sure if they translate to straight power, but I could be wrong. For instance, my company manufactures a 50W tube head and at full clipping into an 8-ohm load the signal measures 71Vp-p.
You do not have the required permissions to view the files attached to this post.
Re: Ampeg V5 to Hiwatt DR103 Conversion Project
Swapping the OT primaries solved it! Thank you to Stevem and xtian for your help!
There's another issue somewhere in the preamp because the audio signal isn't making it all the way through, but I think that's just either a bad tube or the conductor in my shielded wire is getting shorted to ground. I'll investigate further tomorrow. Thanks again, gents!
There's another issue somewhere in the preamp because the audio signal isn't making it all the way through, but I think that's just either a bad tube or the conductor in my shielded wire is getting shorted to ground. I'll investigate further tomorrow. Thanks again, gents!
-
Stevem
- Posts: 4750
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Ampeg V5 to Hiwatt DR103 Conversion Project
Good news to hear!
Now just trace down the signal flow issue.
Now just trace down the signal flow issue.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!