Ft. Tuthill 80 Transceiver Build — Update 2

Ran into some dif­fi­cul­ties exac­er­bat­ed by my own stub­born­ness. Volt­ages were not good on the NE5532 U4 and U5. Upset, I asked for help on the Yahoo forum. I decid­ed to step away for a week (had work com­mit­ments in any case.) Cooled down, heed­ed advice and got it fixed! Trou­bleshoot­ing thread fol­lows (tl;dr) …

Tue Mar 302010 1:23 pm

I will appre­ci­ate any assis­tance with my Ft. Tut-80 build. Let me start by mak­ing an admis­sion (#1): I mea­sured volt­ages on V1 that were in error but ques­tioned my results. As such I forged ahead with the rest of the build since the sys­tem seemed to behave cor­rect­ly. I am sor­ry I did not stop and ask these questions.

Symp­toms are follows:

1. Sidetone and Spot­ting func­tion works
2. Was able to hear and estab­lish VFO fre­quen­cy on my “Big Rig”…currently set to 3584 (pend­ing secur­ing of L9 with wax)
3. No received signals

Things were pro­ceed­ing fine until I go to the instal­la­tion of IC4. I had been test­ing with a wall wart rat­ed at +12V 4A. Admis­sion #2: I mea­sured the actu­al volt­age and found it to be +17V!

Upon instal­la­tion of IC4, volt­ages were not match­ing either there or IC1 (where they were fine before). As I men­tioned, I con­tin­ued with the build since the CPU-based func­tions were OK (I think I real­ize the errors of my ways).

I am not list­ing the volt­ages here in this mes­sage as I need to ask how best to debug. I have checked com­po­nent loca­tions and val­ues and all look good. I have checked sol­der­ing and all looks fine. I have been very care­ful to make sure tem­po­rary con­nec­tions have not been short­ed. Trans­form­ers wind­ings have been checked and counted.

Is it pos­si­ble my mis­take of run­ning 17V has dam­aged a com­po­nent? Is it pos­si­ble the NE5532s were toast­ed some­how (U3, U4…and pos­si­bly U1). What would influ­ence low volt­ages on U1 if this IC was not damaged?

I appre­ci­ate your thoughts (and don’t build your Tut-80 like I did. I did and now I have problems!)

Re: Trou­bleshoot­ing Help

Should read U1, not V1. Sor­ry for mis­takes caused by haste.

Brad WF7T


Tue Mar 302010 2:35 pm

Yikes! I don’t want to be pre­sump­tious ‑but I am con­cerned about pos­si­ble bat­tle dam­age. Wal-warts are often envi­sioned to draw a lot of cur­rent, to bring the volt­age down since these things typ­i­cal­ly lack reg­u­la­tion. The tut on receive of course draws tiny current.

The datasheet implies the NE5532 can han­dle 22 volts — but I can imag­ine some caveat’s involved.

I sug­gest wait­ing for some­one more famil­iar with the design and com­po­nents to guide you into locat­ing what is most like­ly to be dam­aged. Even if you have NE5532 spares you could do dam­age doing an unnec­es­sary repair.

To be a use­ful pow­er sup­ply to test projects like this — you must add a reg­u­la­tor with appro­pri­ate capac­i­tors on it. A set of bat­ter­ies with enough volt­age can be used as a pow­er sup­ply, FWIW.

Les­son learned — check out all ‘unknown’ pow­er sources with a DVM. I can imag­ine learn­ing some­thing new myself on my next trip to the work­bench, if I pay attention.



Yes I did indeed learn my les­son. I was shocked (and ashamed since I know better…I least I thought so…) I am now only using a stiffly reg­u­lat­ed bench supply.I accept pos­si­ble bat­tle dam­age as you say, but I don’t want to pre­scribe this as the fail­ure mode either…at least con­cern­ing the op amps. I agree with you Curt, no unsol­der­ing until I get some more input.

I do appre­ci­ate your comments!

73 Brad “try­ing to not let the blue smoke out” WF7T


As far as dam­age goes, I would think it would be pret­ty lim­it­ed. First, check to see if the 5v reg­u­la­tor is work­ing ok. Check 5v at pin 16 on IC6, the 74HC4053 mux part. I would expect that the 5v reg­u­la­tor is ok as it is good for 30v.If you can hear the sign on “v1” on pow­er up, the PIC is ok and IC3 is like­ly ok.

If you have IC 3 and IC 4 installed and they are work­ing ok, pin 1 on both IC3 and IC4 and in 7 of IC4 should be 5v. Pin 7 of IC3 should be 4.1v. If these are ok, the op-amps should be ok. The op-amps are good for 36v, so I don’t real­ly expect a prob­lem there.

The reg­u­la­tor pro­tects a lot of things. The two places where you could have prob­lems is IC1 (CA3086) which is rat­ed to 15v, and the 11v fil­ter tran­sis­tor Q1 (2N3904). Check U1 pin 5 to see if you have about 1v less than your input sup­ply. If the input is 12v, you might see 11v here.
If you see some­thing like 5v either Q1 is blown or U1 is short­ed or both. Let me know what you see.

If you could send your volt­ages for U1 as well as what you sup­ply volt­age is, I could see if there is a prob­lem. The expect­ed volt­ages are list­ed in the man­u­al assum­ing a 12v input. Look at the volt­ages on page 13 of the part 2 man­u­al on line. The volt­ages there are cor­rect except that pin 5 ought to be 11v because L1 was not installed yet when that read­ing was tak­en. The prob­lem is that with the VFO con­nect­ed, these volt­ages will have both a DC and an AC com­po­nent (due to the VFO run­ning through it), so the volt­ages may move depend­ing on how the AC volt­ages affect you meter.

I real­ly do not expect 17v to affect that much (U1 and maybe Q1), so this should not be a huge hit.

- Dan, N7VE


Dan, thanks so much for tak­ing time to review and respond. Here is what I measured…

Sup­ply Volt­age = 13.7v

Pow­er up sends “v1

IC6 Pin 165v

IC3 Pin 1 = 1.3v
IC3 Pin 7 = 4.1v

IC4 Pin 1 = 0.7v
IC4 Pin 7 = 0.3v

IC1 Pin 1 = 0.1v
IC1 Pin 2 = ‑0.3v
IC1 Pin 3 = 0.1v
IC1 Pin 4 = 0.9v
IC1 Pin 5 = 0.1v
IC1 Pin 6 = 2.4v
IC1 Pin 7 = 1.6v
IC1 Pin 8 = 8.6v
IC1 Pin 90v
IC1 Pin 100v
IC1 Pin 1113v
IC1 Pin 120v
IC1 Pin 130v
IC1 Pin 1413v

Q1: emit­ter 13v
Q1: base ~0.1v
Q1: col­lec­tor ~0.1v

Some wacky volt­ages for cer­tain. Your thoughts are appreciated…

73 Brad WF7T


The 5v reg­u­la­tor looks good, the PIC12F508 is good, IC3 must be ok, at least the sec­ond half. On the schemat­ic, IC4B is biased from 5v from R16 and C20. Check the volt­age at this point. That 5v bias­es IC4b, whose out­put bias­es IC4a, whose out­put bias­es IC3A. If the volt­age input to IC4B pin 5 is low, this string of three op-amps in a row will also have a low volt­age out­put. The out­put volt­age of one stage should be the same as its DC input volt­age which should be 5v. Look around R16, R17, R18, C22, C23, C21 for shorts, or bridges or to see if you have a joint you for­got to sol­der (it happens).

I take it that the input to Q1 (col­lec­tor) is 13v and that the base and emit­ter are zero. Q1 seems either shot or has an open cir­cuit. Check from IC1 pin 5 to ground and see if you have a short. The first two tran­sis­tors in IC1(pins 1, 2, 3, 4, 5) do not look good. It may be that sim­ply replac­ing Q1 will fix this. Tran­sis­tor pins 6, 7, 8 of IC1 looks good. The oth­er two tran­sis­tors of U1 will not do any­thing unless the rig is keyed. If the finals are not installed, you can do the key­ing test and check these transistors.

If there is not a short to ground as seen from IC1 pin 1, replac­ing Q1 with any NPN type tran­sis­tor of the same pin out (2N4401, 2N22222N3904, etc) will work. This stage requires noth­ing spe­cial, just plain Jane gener­ic NPN tran­sis­tor. It is a rip­ple reduc­tion cir­cuit. Its goal is to pro­vide addi­tion­al iso­la­tion from the sup­ply to the first cou­ple of low lev­el stages so that we can avoid feed back from the out­put audio stages to the input audio stages via the sup­ply volt­age (aka, “howl”). It helps a lot.

It may be that replac­ing Q1 is all you need. Q1 is easy to blow, but it is also easy to replace. If you don’t’ have a replace­ment part, I can send you one. If you use a replace­ment (like a 2N2222) Google on line for the data sheet for the 2N3904 and your replace­ment part and dou­ble check that the pin out is the same.

- Dan, N7VE


Took a while for me to get back to this due to work com­mit­ments. Dan, thank you for this.

For the sake of accu­ra­cy I iden­ti­fied and mea­sures the volt­ages at Q1 (2N3904) as I thought I got them incorrect:

Q1 E: 0.14v
Q1 B: 13.05v
Q1 C: 13.05v

volt­ages at R16: 2.94v

Check from IC1 pin 5 to ground and see if you have a short = I mea­sured open.

Tak­ing mea­sure­ments with a Fluke 8062A True RMS Multimeter…

I have not replaced Q1 as of this mes­sage (although I do have a stash of generic
NPNs of some sort.) Did­n’t want to do that yet once I mea­sured again at Q1 and
oth­er places.

Sol­der joints look ok at this point and no shorts noticed in the areas you rec­om­mend­ed searching.

Replac­ing Q1 seems like the next course of action, do you agree?

73 Brad WF7T


ah HA! Replaced Q1 with anoth­er NPN (an old Radio Shack 2N2222 clone I have had around in le Junque Box for years) and the volt­ages test­ed very nicely!

Con­nect­ed to my G5RV and I hear beau­ti­ful sig­nals from the Geor­gia QSO Par­ty tonight. I must say I am very pleased at the dynam­ic range of this rig! Bone-crush­ing sig­nals right next to ESP-level…I can hear them all with­out any nasty pump­ing and crunch­ing. I knew this was going to be a great RX…totally exceeds my expectations!

I am going to fin­ish my TX test­ing tomor­row, but want­ed to report my suc­cess and absolute satisfaction…thanks to Dan and all…

73 Brad WF7T

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